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vertical line Table of Contents Alphabetical Index of Diseases and Injuries Explanation of Disease Classification

The Disease Classification

ICD-9-CM is totally compatible with its parent system, ICD-9, thus meeting the need for comparability of morbidity and mortality statistics at the international level. A few fourth-digit codes were created in existing three-digit rubrics only when the necessary detail could not be accommodated by the use of a fifth-digit subclassification. To ensure that each rubric of ICD-9-CM collapses back to its ICD-9 counterpart the following specifications governed the ICD-9-CM disease classification:

Specifications for the Tabular List

1. Three-digit rubrics and their contents are unchanged from ICD-9.

2. The sequence of three-digit rubrics is unchanged from ICD-9.

3. Unsubdivided three-digit rubrics are subdivided where necessary to:
a) Add clinical detail
b) Isolate terms for clinical accuracy

4. The modification in ICD-9-CM is accomplished by the addition of a fifth digit to existing ICD-9 rubrics.

5. The optional dual classification in ICD-9 is modified.
a) Duplicate rubrics are deleted:
1) Four-digit manifestation categories duplicating etiology entries.
2) Manifestation inclusion terms duplicating etiology entries.
b) Manifestations of diseases are identified, to the extent possible, by creating five-digit codes in the etiology rubrics.
c) When the manifestation of a disease cannot be included in the etiology rubrics, provision for its identification is made by retaining the ICD-9 rubrics used for classifying manifestations of disease.

6. The format of ICD-9-CM is revised from that used in ICD-9.
a) American spelling of medical terms is used.
b) Inclusion terms are indented beneath the titles of codes.
c) Codes not to be used for principal tabulation of disease are printed with the notation, "Code first underlying disease."

Specifications for the Alphabetic Index

1. Format of the Alphabetic Index follows the format of ICD-9.

2. When two codes are required to indicate etiology and manifestation, the manifestation code appears in brackets, e.g., diabetic cataract 250.5X [366.41]. The etiology code is always sequenced first followed by the manifestation code.


The ICD-9-CM Tabular List for both the Disease and Procedure Classification makes use of certain abbreviations, punctuation, and other conventions which need to be clearly understood.


NEC Not elsewhere classifiable. The category number for the term including NEC is to be used only when the coder lacks the information necessary to code the term to a more specific category.

NOS Not otherwise specified. This abbreviation is the equivalent of "unspecified."


[ ] Brackets are used to enclose synonyms, alternative wordings, or explanatory phrases.
() Parentheses are used to enclose supplementary words which may be present or absent in the statement of a disease or procedure without affecting the code number to which it is assigned.
: Colons are used in the Tabular List after an incomplete term which needs one or more of the modifiers which follow in order to make it assignable to a given category.


Format: ICD-9-CM uses an indented format for ease in reference.

Instructional Notations


This note appears immediately under a three-digit code title to further define, or give example of, the contents of the category.


Terms following the word "excludes" are to be coded elsewhere. The term excludes means "DO NOT CODE HERE".

Use additional code

This instruction is placed in the Tabular List in those categories where the user will need to add further information (by using an additional code) to give a more complete picture of the diagnosis or procedure.

Code first underlying disease:

This instructional note is used for those codes not intended to be used as a principal diagnosis, or not to be sequenced before the underlying disease. The note requires that the underlying disease (etiology) be recorded first and the particular manifestation recorded secondarily. This note appears only in the Tabular List.


To code accurately, it is necessary to have a working knowledge of medical terminology and to understand the characteristics, terminology, and conventions of the ICD-9-CM. Transforming verbal descriptions of diseases, injuries, conditions, and procedures into numerical designations (coding) is a complex activity and should not be undertaken without proper training.

Originally coding was accomplished to provide access to medical records by diagnoses and operations through retrieval for medical research, education, and administration. Medical codes today are utilized to facilitate payment of health services, to evaluate utilization patterns, and to study the appropriateness of health care costs. Coding provides the bases for epidemiological studies and research into the quality of health care.

Coding must be performed correctly and consistently to produce meaningful statistics to aid in the planning for the health needs of the Nation.


1. Always consult Volume 2, Alphabetic Index to ICD-9-CM first.
Locate the main entry term. The Alphabetic Index is arranged by condition. Conditions may be expressed as nouns, adjectives, and eponyms. Some conditions have multiple entries under their synonyms. Select the appropriate code.
2. Refer to Volume I of the ICD-9-CM locating the selected code.
Be guided by any exclusion notes or other instructions that would direct the use of a different code from that selected in the Index for a particular diagnosis, condition, or disease.
3. Read and be guided by the conventions used in the Tabular List (Volume 1, ICD-9-CM).
As reference for use by researchers and to maintain comparability with its parent, the ICD-9, a list of three-digit ICD-9-CM categories is given in Appendix E. While these categories form natural statistical groupings, they cannot substitute for the required five-digit ICD-9-CM code.


Questions regarding the use and interpretation of the International Classification of Diseases, 9th Revision, Clinical Modification can be directed to any of the organizations listed below.
Central Office on ICD-9-CM
American Hospital Association
1 North Franklin
Chicago, Illinois 60606

National Center for Health Statistics
Centers for Disease Control and Prevention
Department of Health and Human Services
3311 Toledo Road
Hyattsville, Maryland 20782

Centers for Medicare & Medicaid Services
Division of Prospective Payment System
Office of Hospital Policy
7500 Security Blvd., C5-06-27
Baltimore, Maryland 21244-1850





The ICD-9-CM Coordination and Maintenance Committee

Characteristics of the ICD-9-CM

The Disease Classification

Alphabetical Index of Diseases

Table of Drugs and Chemicals

Index To External Causes of Injury (E Code)

Classification of Procedures

Index to Procedures

Appendix A:
Morphology of Neoplasms

Appendix C:
Classification of Drugs by American Hospital Formulary Services List Number and their ICD-9-CM Equivalents

Appendix D:
Classification of Industrial Accidents According to Agency

Appendix E:
List of Three-Digit Categories

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