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. The DSM-IV, for example, "applies the term not otherwise specified (NOS) to a disorder or disturbance that does not meet the criteria for the specific disorders already discussed". 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". 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. Examples This classification is commonly used in psychiatric diagnoses, such as in: DD-NOS, depressive disorder ED-NOS, eating disorder MD-NOS, mood disorder PD-NOS, personality disorder PDD-NOS, pervasive developmental disorder Psychotic disorder not otherwise specified It is also used in the conditions: PTCL-NOS, peripheral T-cell lymphoma not otherwise specified Adenocarcinoma not otherwise specified The ICD-10 also uses this phrase for various things, such as: Fall from, out of or through building, not otherwise specified (W13.9) 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.". References International Classification of Diseases Medical terminology