The objective was to use various somatic parameters as basis for investigating the physical health of older adults with severe mental illnesses (SMI). A cross‐sectional study design is performed by using baseline data from the Physical Health in SMI‐elderly (PHiSMI‐E) study. Data were collected using the Nursing Monitoring of Somatic Status and Lifestyle – Mental Health instrument in adults aged over 60 with SMI in a large Dutch mental health institute. Ninety‐nine elderly SMI patients were included. Somatic comorbidity (84.8%), use of somatic medication (77.7%) and polypharmacy (67.7%) were prevalent. Extrapyramidal symptoms were experienced by 51% of patients, mainly in the subgroup with psychotic disorders (75.6%). Unhealthy diet was reported in 16.2%, obesity in 27.3%, and physical inactivity in 57.6%. Fatigue (67.7%) and dry mouth (66.6%) were the commonest reported physical symptoms. Mean VAS score (scale 0–10) indicating participants’ self‐perceived physical health was 6.7 (SD ± 1.6). After division of the total patient group into tertiles based on the VAS scores, the lowest tertile was characterized by less physical activity, unhealthier diet, more use of medication, more fatigue, somnolence, and inner agitation. In conclusion, impaired physical health status was common in these older patients with SMI. Although they had more psychiatric and somatic comorbidity than adult SMI patients described in the literature, they had a healthier lifestyle. To reduce morbidity and premature mortality in these frail patients, it is essential that healthcare providers are aware of the high prevalence of somatic comorbidity and symptoms, and of their interactions with the psychiatric disorders. This study improves our understanding of differences in vulnerability factors of older patients with SMI. The (early) detection of somatic comorbidities may improve long‐term health outcomes of these patients.