Changes in care in short-term general hospitals were monitored for three vulnerable subgroups of Medicare psychiatric patients: (1) those more than 75 years old, (2) those with comorbidities, and (3) those with one or more secondary diagnoses of psychiatric or substance abuse problems. Patterns of care studied for changes following institution of the Medicare Prospective Payment System (PPS) were volume of cases, average length of stay, discharge locations, and readmission rates. Results indicate that the changes occurring for the three subgroups were similar to the changes occurring for all Medicare psychiatric patients. After PPS was introduced in 1983, the average length of stay decreased, and a greater proportion of patients were discharged to other hospitals or home health care providers; however, rates of readmission to the same hospital did not increase.