Metabolic profile of olanzapine as compared to haloperidol has been evaluated much less comprehensively in bipolar than in schizophrenic patients. Medical records of 343 patients who completed a 3-year treatment with haloperidol or olanzapine were retrospectively reviewed, and metabolic outcomes were evaluated. Twenty-three percent of patients fulfilled MetS criteria with a point prevalence of 25.3% in bipolar and 21.2% in schizophrenic group; 20.3% of schizophrenics treated with haloperidol and 22.4% of those treated with olanzapine developed MetS, which was detected, instead, in 17.1% of haloperidol-treated bipolar patients and 32.9% of those treated with olanzapine. Significant changes were detected overtime in fasting cholesterol, systolic BP, BW and BMI; some of these parameters at the 3-year follow-up presented more severe changes with olanzapine than haloperidol in both diagnostic groups. Overall, a significant number of subjects fulfilled MetS criteria in the first month of treatment, but only in schizophrenics olanzapine was faster than haloperidol in inducing such an effect. These data suggest that haloperidol and olanzapine increase the risk for MetS in both schizophrenic and bipolar patients with a higher prevalence for olanzapine only in bipolar patients. Morever, as compared to haloperidol, olanzapine has a faster dismetabolic action in schizophrenic but not in bipolar patients.