Objectives: Obstructive sleep apnoea (OSA) may be more common in people with schizophrenia compared to the general population, but the relative prevalence is unknown. Here, we determine the relative prevalence of severe OSA in a cohort of men with schizophrenia compared to representative general population controls, and investigate the contribution of age and body mass index (BMI) to differences in prevalence. Methods: Rates of severe OSA (apnoea–hypopnoea index > 30) were compared between male patients with schizophrenia and controls from a representative general population study of OSA. Results: The prevalence of severe OSA was 25% in the schizophrenia group and 12.3% in the general population group. In subgroups matched by age, the relative risk of severe OSA was 2.9 (p = 0.05) in the schizophrenia subjects, but when adjusted for age and BMI, the relative risk dropped to 1.7 and became non-significant (p = 0.17). Conclusions: OSA is prevalent in men with schizophrenia. Obesity may be an important contributing factor to the increased rate of OSA.