This multicenter, uncontrolled, naturalistic study evaluated the effectiveness and tolerability of 6 months of treatment with ziprasidone in 1266 patients with a diagnosis of schizophrenia. The percentage of responders (at least 30% reduction in PANSS total score) in the primary analysis sample (n=1022) was 47.3% (95% CI 44.2-50.4) at the end of the study. Patients showed a significant and clinically relevant reduction in the PANSS total, positive, negative and general psychopathology subscales scores (effect size of 1.60, 1.83, 0.62 and 1.40 respectively). Overall, 453 (35.8%) patients withdrew from the study; 9.3% withdrew owing to adverse events. Ziprasidone doses greater than 120 mg/day were associated with a lower risk of discontinuation for any cause (OR 0.46, 95% CI 0.33-0.65) Ziprasidone was well tolerated. Most common side effects were: insomnia, somnolence and nervousness. The effectiveness and tolerability of ziprasidone in clinical practice are consistent to those previously shown in the more restricted and homogeneous populations of clinical trials.