The aim of this study was to evaluate the long-term efficacy of haloperidol in autistic children and to determine whether discontinuous drug administration was as effective as continuous drug administration. Sixty children, 48 males and 12 females, ages 2.3 to 7.9 years ( 5.1) completed the study. They received haloperidol over a period of 6 months followed by a 4-week drug withdrawal/placebo period. Haloperidol remained effective, and the discontinuous treatment schedule did not diminish its efficacy. Children with prominent symptoms of irritability, angry and labile affect, and uncooperativeness were the best responders to haloperidol.