 Risperidone will be started at 0.5 mg at bedtime for 4 days and, if the current dosage is tolerated as evidenced by no more than mild sedation, no EPS or other moderate to severe AEs, and if there are continued behavioral symptoms, the dose will be increased to 1 mg at bedtime for an additional 4 days. If tolerated and indicated, 0.5 mg will be added in the AM for a daily total of 1.5 mg. After that, dosages may be increased if there does not appear to be an adequate clinical response. Dosage will not be increased if there are side effects e.g. excessive sedation, salivation, EPS, lactation and may be decreased if it is not tolerated. If the investigator determines that a significant adverse reaction occurs or if the subject or his or her family wants to stop the study, the medication will be tapered or stopped depending on the dose and reason for stopping and the subject will be offered alternative treatment at the M.I.N.D. Institute Clinic or referred elsewhere. This dosing schedule mirrors that used in the two recent positive trials of risperidone for treating severe behavioral problems in autism McCracken et al., 2002; Shea et al., 2004. 