Posttransplant lymphoproliferative disease (LPD) is a serious complication, associated with considerable morbidity and mortality. Herein the authors report their experience with LPD in a series of pediatric liver recipients (from 1986 to 1993). A total of 95 transplants were performed in 78 patients. Only the 66 patients who survived at least 30 days were included in the analysis. There were seven cases of LPD (incidence, 10.6%). Seven of the 43 patients who received OKT3 had LPD, compared with none of the 23 patients who did not receive OKT3 (P < .05). The total cumulative dose and the duration of therapy both correlated with occurrence of LPD. However, the dose per kilogram did not correlate with the development of LPD. The median time from transplant to diagnosis was 90 days. All cases were immuoblastic B-cell lymphomas, and all tumors were positive for the Epstein-Barr viral genome (EBV). Four patients never treated for LPD died; it was discovered incidentally during autopsy in two, during retransplantation in one, and within 5 days of death in one. The other three were treated with decreased immuno-suppression, acyclovir, gamma globulin, and alpha-interferon. All three were cured of LPD, but one died of neurological complications after retransplantation. LPD may be interpreted as a symptom of a chronically overimmunosup pressed state, associated with a high mortality, from a variety of causes. LPD should be suspected for any patient whose clinical condition is deteriorating with no clear evidence of rejection, and should lead to a decrease in the amount of immunosuppression used. Copyright (C) 1994 by W.B. Saunders Company