This study assessed the efficacy of ziprasidone for the treatment of schizoaffective disorder. Data were taken from subsets of patients with schizoaffective disorder, derived from two separate double-blind, placebo-controlled, parallel-group, multicenter studies. A total of 115 hospitalized patients with an acute episode of schizoaffective disorder were randomly assigned to receive either fixed oral doses of ziprasidone 40 mg/day (N = 16), 80 mg/day (N = 18), 120 mg/day (N = 22), 160 mg/day (N = 25), or placebo (N = 34) for 4 to 6 weeks. Mean baseline-to-endpoint changes in Brief Psychiatric Rating Scale (BPRS) total, BPRS Core, Clinical Global Impressions Severity scale (CGI-S), BPRS Depressive, BPRS Manic, and Montgomery-Åsberg Depression Rating Scale total scores were compared between the placebo and ziprasidone groups. Neurological (Simpson-Angus, Barnes Akathisia, Abnormal Involuntary Movement Scale [AIMS]) and other side effects were also assessed. Significant dose-related improvements on all primary efficacy variables (BPRS total, BPRS Core, CGI-S) and for BPRS Manic items were observed with ziprasidone treatment in a combined analysis of data from both studies (p≤ 0.01). Ziprasidone 160 mg/day was significantly more effective than placebo in improving mean BPRS total, BPRS Core, BPRS Manic, and CGI-S scores (p< 0.05). At 120 mg/day, ziprasidone was significantly more effective than placebo in improving mean CGI-S scores (p< 0.05). The incidence of individual adverse events was generally low in all treatment groups and was not dose-related. In addition, no significant differences were observed between baseline-to-endpoint mean changes in Simpson-Angus and AIMS scores with placebo or ziprasidone 40 to 160 mg/day. These results suggest that ziprasidone may have efficacy in the treatment of affective as well as psychotic symptoms of schizoaffective disorder, with a low side-effect burden.