Estimated compliance rates of 40 to 50% are common among psychiatric outpatients. Likely noncompliers in the acute phase of illness include manic patients, paranoid schizophrenics, and the profoundly depressed. Noncompliance during the long-term prophylactic or maintenance treatment phase tends to increase with the passage of time. The cause of noncompliance is multifactorial. The use of long acting parenteral neuroleptic agents may help decrease the incidence of noncompliance, although documentation is difficult to obtain. Because of the risk of tardive dyskinesia, the lowest possible dose of the depot medication should be used. Studies are now under way to ascertain minimal effective doses necessary to prevent relapse and minimize adverse effects.