This study is a placebo-controlled, double-blind study (neither the investigators nor patients know if the treatment being given is risperidone or an inactive substance, placebo). Patients will be asked to participate for 6 to 8 months. For the first 8 weeks, patients will receive either risperidone or placebo, randomly chosen. At the end of the 8 weeks, those patients who have improved and were on risperidone will be asked to continue on this medication for another 4 months. The last two months of the study are again double-blind (neither patients nor investigators know treatment). Patients will either continue risperidone treatment or be gradually tapered from risperidone (placebo-substitution). This blinded discontinuation phase will last 2 months during which patients will be closely monitored for recurrence or worsening of symptoms. Patients who have been treated with placebo in the first 8 weeks of the study and have not improved will be treated with risperidone. Weekly visits are required for the first 8 weeks of the study, monthly visits for the following 4 months, and weekly visits during the last 2 months of the study.