This section includes symptoms, signs, abnormal results of laboratory or other investigative procedures, and ill-defined conditions regarding which no diagnosis classifiable elsewhere is recorded.

Signs and symptoms that point rather definitely to a given diagnosis are assigned to some category in the preceding part of the classification. In general, categories 780-796 include the more ill-defined conditions and symptoms that point with perhaps equal suspicion to two or more diseases or to two or more systems of the body, and without the necessary study of the case to make a final diagnosis. Practically all categories in this group could be designated as "not otherwise specified," or as "unknown etiology," or as "transient." The Alphabetic Index should be consulted to determine which symptoms and signs are to be allocated here and which to more specific sections of the classification; the residual subcategories numbered .9 are provided for other relevant symptoms which cannot be allocated elsewhere in the classification.

The conditions and signs or symptoms included in categories 780-796 consist of: (a) cases for which no more specific diagnosis can be made even after all facts bearing on the case have been investigated; (b) signs or symptoms existing at the time of initial encounter that proved to be transient and whose causes could not be determined; (c) provisional diagnoses in a patient who failed to return for further investigation or care; (d) cases referred elsewhere for investigation or treatment before the diagnosis was made; (e) cases in which a more precise diagnosis was not available for any other reason; (f) certain symptoms which represent important problems in medical care and which it might be desired to classify in addition to a known cause.