The rehospitalization experience of Medicare beneficiaries undergoing coronary artery bypass surgery or percutaneous transluminal coronary angioplasty in 1986 and 1987 was studied by following 53,715 patients who underwent coronary artery bypass and 28,817 patients who underwent angioplasty for 1 year using Medicare hospital claims data. The 1-year rehospitalization rate after bypass and angioplasty was 629 and 863 per 1,000, respectively, compared to a rate of 607 for the Medicare patient population in general. About 45% of rehospitalizations after bypass and two thirds after angioplasty were in categories determined by an expert panel to be probably related to the original procedure. After angioplasty, there were 61 discharges per 1,000 for bypass surgery and 140 per 1,000 for a repeat angioplasty. Rehospitalization rates for coronary artery bypass surgery after angioplasty were significantly lower for female and black patients who underwent angioplasty. The volume of rehospitalization after revascularizations makes it an important outcome measure. Medicare administrative records provide a unique source of information on rehospitalizations and make possible the monitoring of trends in the frequency and outcomes of coronary revascularization. The lower rates of bypass surgery after angioplasty for black and female patients are in line with other studies and bear further investigation.