This was a randomized, flexible-dose, rater-blind, parallel-group, quasi-naturalistic trial comparing the efficacy, safety, and tolerability of quetiapine, risperidone, and olanzapine in patients with schizophrenia hospitalized for severe psychotic symptoms. Seventy-five patients were randomized to quetiapine (n =25), risperidone (n =25), or olanzapine (n =25). Mean doses at Week 8 were: 590.0 mg/day quetiapine; 5.1 mg/day risperidone; 15.1 mg/day olanzapine. Four quetiapine, five risperidone, and five olanzapine patients discontinued prior to Week 8. There were no significant differences between groups in the primary efficacy measures of improvement from baseline in Positive and Negative Syndrome Scale (PANSS) total score at Week 8 in the per protocol (PP) population and the number of completers who experienced ≥ 40% improvement on the same scale. PP and intent-to-treat analyses showed significant improvement from baseline in each component of a PANSS-derived battery, without significant differences between treatments. No quetiapine patients, one risperidone, and four olanzapine patients reported an adverse event (AE) of moderate intensity; no severe AEs were reported. A linear mixed model for repeated measures showed an effect of treatment on body weight, with significant differences favoring quetiapine over risperidone and olanzapine. Simpson–Angus Scale scores were significantly worse with risperidone compared with both olanzapine and quetiapine at Week 3 and compared with quetiapine thereafter. Use of concomitant medications for anxiety or tension was significantly less frequent with quetiapine. In conclusion, quetiapine, risperidone, and olanzapine have similar efficacy in schizophrenia, but there are drug-specific differences for some AEs and in the use of concomitant medication that differentiate these agents.