The results of an evaluation of a predischarge utilization review program [PDUR] for Medicaid Patients are presented. A group of hospitals in Allegheny County, Pennsylvania, participated in this program on a voluntary basis prior to the program's being mandated statewide. All other hospitals in the county experienced retrospective review of Medicaid cases. Our analysis incorporates both types of hospitals in a quasi-experimental design. We found that during the period studied the length of stay of Medicaid patients fell proportionately more than that of the Blue Cross patients in both groups of hospitals; the relative decrease in the length of stay began to occur prior to the introduction of the PDUR program, but no differential effect of the PDUR review process could be demonstrated. The decline in the length of stay was, however, more continuous and smooth in those hospitals participating in the program.