We report the experience with Pneumocystis carinii lung infections in the 109 children undergoing liver transplantation at our hospital between August, 1985 and May, 1989. PCP developed in 9 of the 86 patients (10%) surviving > or = 6 weeks after transplantation and not receiving P carinii chemoprophylaxis. Of the 59 patients undergoing BAL 2 or more weeks after transplantation there were 16 specimens from 14 patients (24%) positive for P carinii. These patients had a spectrum of illness ranging from asymptomatic to severe pneumonia requiring mechanical ventilation. The mean interval from first transplantation to bronchoalveolar lavage positive for P carinii was 24.9 weeks and the mean interval to first PCP was 28.0 weeks. The earliest and latest occurrences of PCP were 7 weeks and 73 weeks, respectively, after transplantation. There were no complications attributed to BAL.