A sample of 388 primary care patients in a Swedish health district were screened for psychiatric illness using the Hopkins Symptom Check List HSCL-25. General practitioner (GP) ratings of psychiatric illness and patient ratings of psychosocial problems were also included. Data concerning the patients' utilization of care and health insurance were recorded. According to the HSCL-25, 30.2% of the patients were probable psychiatric cases and 19.2% were psychiatric cases in need of treatment. According to GPs' independent ratings, 12.3% of the patients suffered from psychiatric illness requiring treatment. Psychiatric cases according to HSCL-25 were more often women, divorced, unemployed and living alone. During the year preceding index contact, psychiatric cases showed a higher utilization of primary care, as well as other somatic care. They also had more sick leave. Psychiatric cases perceived higher levels of psychosocial problems in areas of unemployment, work situation, private economy, child care and social isolation. The results of the study point to the interaction of psychological impairment, environmental stress and lack of social support in producing psychiatric illness.