We evaluated relapse in patients with stable, chronic schizophrenia over a 1-year period; inpatients were randomized to ziprasidone 40 mg/day (n = 72), 80 mg/day (n = 68), 160 mg/day (n = 67) or placebo (n = 71). The probability of relapse (Kaplan-Meier) at 1 year was significantly lower in the ziprasidone 40, 80, and 160 mg/day groups (43%, 35% and 36%, respectively) compared to placebo (77%; P = 0.002, P < 0.001 and P < 0.001, respectively). In those patients who remained on treatment for at least 6 months, only 9% subsequently relapsed on ziprasidone compared to 42% on placebo (P = 0.001). All three doses of ziprasidone were significantly superior to placebo on Positive and Negative Syndrome Scale (PANSS) efficacy variables (all P < 0.05). Ziprasidone was associated with a significantly greater mean improvement in the PANSS negative symptom subscale compared to placebo (P < 0.05). Discontinuation due to adverse events was similar with ziprasidone and placebo. Ziprasidone treatment was indistinguishable from placebo in assessments of movement disorders and was not associated with weight gain or cardiovascular abnormalities. These results demonstrate that ziprasidone was effective in reducing the frequency of relapse and was associated with long-term improvement in negative symptoms. Ziprasidone was well tolerated in this population of patients with chronic, stable schizophrenia.