Coronary disease after cardiac transplantation is a major medium and long-term complication in adult patients. In childhood, this is reputed to be rare and, therefore, the authors undertook a study to evaluate its incidence and the role of potential risk factors in this age group. The study included 30 children followed up at least one year after cardiac transplantation and investigated by at least one selective coronary angiography after the first postoperative year. Seventeen patients (57%) had a normal coronary angiography but 13 had coronary lesions (43%). The two groups were compared for age, sex, HLA groups of the donor-recipient couple, the duration of ischaemia of the transplants, cytomegalovirus serology, lipid profile, number of episodes of acute rejection that were treated, the necessity for steroid therapy for more than 3 months, and the blood pressure. The only significant differences, probably inter-related, were the number of rejections treated, greater in the group with coronary lesions (2.23 +/- 1.01 per patient) than in the group with normal coronary arteries (1.53 +/- 1.01 per patient) (p < 0.05) and the necessity of triple therapy with addition of prednisone, greater in the first group (9/13) than in the second (4/17) (p < 0.02). These results show that coronary disease after cardiac transplantation is as common and as early in children as in adults. They strongly suggest an important role of immunological factors. On the other hand, the authors' experience did not confirm the role of other potential risk factors.