Disorder of Infancy, Childhood, or Adolescence Not Otherwise Specified
The Disorder of Infancy, Childhood or Adolescence, Not Otherwise Specified (or NOS) diagnosis is a residual category which is used for children when it is clear that some childhood disorder ought to be diagnosed, but clinicians do not yet have enough information about the child's difficulties to make a more specific diagnosis. Over time, as more diagnostically important information becomes available (e.g., as a result of testing, behavioral observation, medical record review and interviews), it is common practice for NOS diagnoses to be discarded so that more specific diagnoses can be made.
The NOS diagnosis is also made when clinicians encounter a symptom presentation that simply does not fit cleanly into any other known disorder of childhood diagnostic category. When used in this fashion, the NOS diagnosis is treated as a catch-all category where disorders with symptoms that may be similar to other disorders and are significant enough to cause impairment (but do not meet full DSM criteria) may be lumped together.