Objectives : To assess the difference in the volume of psychiatric treatments provided to health insurance inpatients, compared with those on medical assistance(the medical aid program) Korean psychiatric hospitals, and to determine factors which affect the volume of the services. Methods : 21 psychiatrists, from 3 Korean psychiatric hospitals recorded the frequencies psychiatric treatments provided to inpatients in one week (February 18-24, 2002). The records of 329 patients were analyzed through t-tests, and random effectmixed model analyses to define the difference between the two groups, and to find other factors affecting the volume of service. Results : A significant difference in the volume of psychiatric treatments provided was observed between the health insurance and medical assistance groups. The variation in the volume of service between hospitals was prominent, and other factors (gender, agegroup, length of stay and mental disorder)were also found to be significant. The patients on medical assistance received only 70% of the psychiatric treatments of those on health insurance. Conclusions : More effort is required to improve the methods of payment to increase the level of fee scheduling for medical assistance. Further studies on the mechanisms causing these differences in the volume of service are required.