Noncompliance with medication and follow-up care was evaluated in 538 renal, 50 heart, and 13 liver transplant recipients. In a retrospective review of 260 kidney transplant recipients followed from three months posttransplant, the incidence of medication noncompliance was 18%. It was 15% in a prospective study of 196 kidney recipients from 1984 to 1987. Patients most likely to become noncompliant were young and in a lower socioeconomic group. There was no significant difference in the incidence of noncompliance with respect to cadaveric vs. living-related donor kidney source, or in male vs. female patients. There was a higher incidence of noncompliance in blacks and Hispanics, but that may have been due to a higher incidence of lower socioeconomic status in those groups. Noncompliance can occur many years posttransplant and was seen in heart and liver transplant recipients. In the retrospective study, 91% of kidney transplant recipients who were noncompliant with medications and follow-up care either lost their grafts or died. Noncompliant behavior was usually not predictable and was often without an identifiable reason. Efforts to increase compliance, such as better patient selection, more education, and simplified medical regimens may have reduced the incidence of noncompliance in recent patients.