In a naturalistic study of 23 severely and profoundly mentally retarded adult male patients undergoing slow "diagnostic" neuroleptic taper, it was determined that at least 60% could eventually be managed without psychoactive medication. However, many of these demonstrated a remarkably long, but nonetheless transient, period of worsening. This suggests that behavioral deterioration during drug reduction trials does not always indicate a need for chronic neuroleptic maintenance since these behaviors may return to baseline without pharmacological intervention. On the other hand, 40% demonstrated persistent (> 2 years) behavioral worsening. Those individuals who demonstrated persistent deterioration had been generally well controlled on neuroleptics, were somewhat older, and were receiving a higher baseline dose. Most of these persistently worsened subjects currently require some type of psychoactive medication (although only two have been returned to neuroleptics).