People with severe mental illness have a higher rate of premature death than the general population, largely due to primary care preventable diseases. There has been little research on the health profile of this population attending Australian general practices. In this nationwide cross-sectional study, MedicineInsight data for adult patients regularly attending general practices in 2018 were analysed to estimate the prevalence of schizophrenia or bipolar disorders (SBD) and investigate the health profile of people with SBD compared with other patients. Multilevel models clustered by practice (n = 565) and patient, and practice characteristics were created. The prevalence of recorded SBD was 1.91% (95% CI = 1.88%-1.94%) among the 618 849 patients included. Patients with recorded SBD were more likely than other patients to have records of health risk factors, particularly smoking (aOR = 3.8, 95% CI = 3.6-3.9) and substance use (aOR = 5.9, 95% CI = 5.6-6.3), and higher probabilities of comorbidities including cardiovascular diseases (aOR = 1.3, 95% CI = 1.2-1.4), cancer (aOR = 1.1, 95% CI = 1.0-1.2), diabetes mellitus type 2 (aOR = 2.2, 95% CI = 2.0-2.3), chronic kidney diseases (aOR = 1.7, 95% CI = 1.5-2.0), chronic liver diseases (aOR = 3.3, 95% CI = 2.6-4.0) and chronic respiratory diseases (aOR = 1.7, 95% CI = 1.7-1.8). The higher prevalence of health risk factors and comorbidities among patients with recorded SBD underscores the need for proactive health risk monitoring and preventive care to address this health inequity.