In medicine, not otherwise specified (NOS) is a subcategory in systems of disease/disorder classification such as ICD-9, ICD-10, or DSM-IV.
It is generally used to note the presence of an illness where the symptoms presented were sufficient to make a general diagnosis, but where a specific diagnosis was not made.
[1] The term was introduced because "it is sometimes impossible for the practitioner completing the diagnostic assessment to categorize all the symptoms that a client is experiencing into one diagnostic category".
[2] In the context of mental health diagnoses, four situations have been outlined for which such a diagnosis may be considered appropriate: It is noted, however, that the use of an NOS classification invites scrutiny when billing or seeking reimbursement for practitioners.
[2] This classification is commonly used in psychiatric diagnoses, such as in: It is also used in the conditions: The ICD-10 also uses this phrase for various things, such as: The phrase is also used within the List of UN numbers, where it refers to a generic entry, e.g. "UN 1993: Flammable liquid, N.O.S.".