This investigation estimates and compares, for the first time, the distribution of body mass index (BMI: kg/m(2)) and the prevalence of obesity among Chinese outpatients with schizophrenia treated with antipsychotics. The BMI of 201 outpatients with schizophrenia-spectrum disorders was studied via a cross-sectional naturalistic study. This investigation also compared the BMI of the subjects with a Taiwanese reference population. This investigation found no significant difference in the prevalence of obesity between male and female subjects. The prevalence of obesity among male and female patients in this investigation was, respectively, 2.74- and 2.51-fold greater than the Taiwanese reference population, and the prevalence of severe obesity among male and female patients was 4.66- and 3.53-fold greater than that in the Taiwanese reference population, respectively. The rate of severe obesity was especially high in patients treated with olanzapine. Atypical antipsychotics other than olanzapine did not seem to be more closely associated with obesity or severe obesity compared to typical antipsychotics.