Claims for physical health care among 220 Medicaid enrollees with severe mental illness and 166 Medicaid enrollees who were not enrolled in the public mental health system were compared. Claims for the mentally ill group were 18 percent less than for the group without severe mental illness. Twenty-eight percent of claims for mentally ill patients were for treatment in emergency rooms and ambulances, compared with 11 percent for patients without mental illness; 26 percent of claims for patients without mental illness were for care in outpatient surgical and outpatient hospital settings, compared with 14 percent for mentally ill patients. Results suggest inefficient use of the health care system by mentally ill patients and highlight the need for coordination of care.