ICD - International Statistical Classification of Diseases and Related Health Issues

During the 15th Century, Italy began recording how people died in the form of death certificates and this formed the basis of a document that would record the different disease that would lead to mortality.

It was the plagues that swept through Europe at this time that increased interest in how and why people were dying great advancements in the realms of medical education throughout Europe gained prominence and by the 16th Century, France, the Netherlands and Switzerland had developed boards of health to track epidemics among their cities.

Sir George Knibbs, the eminent Australian statistician, credited François Bossier de Lacroix (known as Sauvages) with the first attempt to classify diseases systematically in his comprehensive treatise, Nosologia methodica.

England passed the Registration Act in 1837 and formed the General Register Office of England and Wales, which had the purpose of gathering information of deceased populations and their various causes of death.

Precursors to the ICD

In 1860, Florence Nightingale made a proposal at the International Statistical Conference which lead to the first model of systematic collection of hospital data and in 1893, the French physician Jacques Bertillon created his “Bertillon Classification of Causes of Death” and unveiled this at the International Statistical Institute conference in Chicago.

Bertillion’s Classification of the Causes of Death was based on the principle of distinguishing between general diseases and those localized to a particular organ or anatomical site, as used by the City of Paris for classifying deaths and was used as the model that was adopted by other countries.

ICD-1, 2 and 3

In 1898, the APHA (American Public Health Association) adopted Bertillion’s classification for Canada, USA and Mexico and called it the International List for the Causes of Death or ICD. The APHA also proposed the document be revised every 10 years.

Bertillon continued to be the driving force behind the 1900, 1910 (The English translation was titled as the International Classification of Causes of Sickness and Death) and 1920 revisions of the ICD. Bertillon died in 1922 and left the ICD leaderless.

ICD-4 and ICD-5

In 1923, Michel Huber was Bertillon’s successor and introduced a resolution to the International Statistics Institute to renew it’s stand and co-operate with other international nations.

The Health Organization of the League of Nations appointed a Commission of Statistical Experts to research the ICD further and created the “Mixed Commission” with an equal number of representatives from the International Statistical Institute and the Health Organization of the League of Nations.

This Commission drafted the proposals for the Fourth (1929) and the Fifth (1938) revisions of the International List of Causes of Death.


The International Health Conference held in New York City in June and July 1946 entrusted the Interim Commission of the World Health Organization (WHO)

In 1948, the First World Health Assembly endorsed the report of the Sixth Revision Conference and adopted World Health Organization Regulations No 1.

The ICD was given the new title of Manual of the International Statistical Classification of Diseases, Injuries, and Causes of Death and was split into two volumes, with volume 2 being the alphabetical list of diagnostic terms coded to the appropriate categories.

ICD-7 & 8

The International Conference for the Seventh Revision of the International Classification of Diseases was held in Paris under the auspices of WHO in February 1955 but the WHO Expert Committee on Health Statistics limited this revision to essential changes and amendments of errors and inconsistencies.

When the Eighth Revision Conference met in Geneva in 1965, their revision was more radical than the Seventh revision but kept the basic classification structure and the philosophy of classification according to their aetiology (the medical term for the determination of cause)

During the years that the Seventh and Eighth Revisions of the ICD were in force, the use of the ICD for indexing hospital medical records increased rapidly and some countries prepared national adaptations which provided the additional detail needed for this application of the ICD.


Initially when the International Conference for the Ninth Revision met in 1975, they had planned to just refresh the ICD, with the document becoming the International Classification of Diseases.

However, with the increased interest in the ICD from specialist bodies that had become interested in using the ICD for their own interests, it was decided to keep the structure the same, but to extend the ICD to include fourth and fifth subdivisions of categories while keeping the three level categories to make the ICD easier to read for those not interested in the detail.

The ICD-9 also included an alternative method of classification for diseases that became known as the dagger and asterisk system and approved the supplementary classifications of Impairments and Handicaps and of Procedures in Medicine for trial purposes.


Even before the International Conference for the Ninth Revision met, the WHO began drafting what would become the ICD-10 since it was realised that the ICD had experienced a great expansion in professionals using it and the structure would need to be revised to cope with that.

It had become clear at this point that the 10 year revision of the ICD was far too short, and although the ICD-10 was due to be issued in 1985, the The Director-General of WHO wrote to the member states and asked to postpone the proposal until 1989.

The Health Assembly adopted the tenth revision in 1990 in the form of resolution WHA43.24 which came into effect in 1993.

The changes culminated in a 63 page document called the Report of the International Conference for the Tenth Revision of the International Classification of Diseases.


The Executive Board at its 144th session considered an earlier version of a report that ended up being suspended before the International Conference called the WHO 72th Assembly which defined ICD as:

“The International Statistical Classification of Diseases and Related Health Problems, commonly referred to as the International Classification of Diseases (ICD), is the global standard classification for mortality and morbidity statistics. Such data, broken down by age, sex and cause of death, constitute the foundation of public health. Progress towards the Sustainable Development Goals and universal health coverage is measured with several cause – specific mortality and morbidity indicators.”

WHO formally launched the process of revising ICD10 in 2007, and the ICD-11 Revision Conference held in Tokyo in 2016 where hundreds of experts from around the world contributed and gave positive feedback to the ICD-11 content and structure. By November 2018, the ICD-11 was approved and training materials provided from May 2019.

The ICD-11 will become active from January 2022.

ICD-11 has it’s own home page at the WHO.

PCS and CM

In the USA, the ICD is divided into two coding systems, the first is called PCS or Procedural Coding System and was developed by the Centers for Medicare and Medicaid Services n conjunction with 3M Health Information Management to track international morbidity and mortality statistics in a comparable way.

The PCS is only used for in-patients in a hospital setting and uses three to seven-digit alphanumeric codes to specify medical procedures. The first digit indicates the section of medical practice (surgery, administration, measuring and monitoring, etc.) and the following digits specify the body system, root operation, body part, approach and the device used. The seventh character is a qualifying digit.

The first 3 characters are taken from the ICD.

The second coding system is called CM or Clinical Modifications and is used in clinical and outpatient settings. In CM coding, the first character can be either a letter or a number, but the rest of the coding is in the form of numbers.

Although the ICD-10 PCS was derived from the ICD-10 it is not compatible with it, and the US has decided not to implement the ICD-11 coding for their PCS system. The ICD-11 will however, replaced ICD-10 CM.