• The potential for unwanted side effects, particularly tardive dyskinesia, following long-term aftercare maintenance with antipsychotic medication has led to serious questioning of its continued use for schizophrenic patients. Does the risk of relapse decline with the passage of time? If so, is the advantage of drug therapy sustained and large enough to justify continued treatment beyond one or two years? More appropriate methods for analyzing the aftercare experience of 374 schizophrenic patients treated with drug or placebo reveals that while the risk of relapse does decline substantially, it remains twice as high for placebo-treated patients than drug-treated patients even after two years of treatment. The prophylactic effect of maintenance chemotherapy appears to be one to two times larger than generally estimated by the less precise "cumulative percentage" method.