Background/purpose Lymphoceles are frequently observed as a surgical complication after renal transplantation. Whereas the frequency, pathogenesis, diagnosis, and treatment of lymphoceles has been well described in adult patients, no data are available for the pediatric age group. Methods Since December 2000; 5 children (2 boys and 3 girls; median age, 6 years; range, 6 to 15 years) of a total of 21 (10 boys and 11 girls; median age, 13 years; range, 2 to 19 years) children undergoing kidney transplantation had a posttransplant lymphocele. The clinical course, renal function, and ultrasonographic appearance of the transplanted kidney of all children were observed in a prospective manner. Results The lymphoceles became obvious between day 13 and 48 (median, 20 days) posttransplantation. Lymphocele size ranged from 2.0 × 3.0 cm to 11.0 × 15.0 cm. They were localized at any site (superior, inferior, lateral, medial, and dorsal) around the transplanted kidney. Four patients had a significant decrease of renal function, in 2 children mild urinary tract obstruction occurred, and 1 patient suffered from considerable abdominal pain. Diagnosis was established by ultrasound scan in all cases. All patients were treated by laparoscopic fenestration of the lymphocele immediately after diagnosis, except 1 patient, in whom fenestration was not done until 10 months later. Operating time ranged from 45 to 90 minutes (median, 62 minutes). No intraoperative or postoperative complication occurred. Renal function, urinary tract obstruction, and pain recovered soon after operation in all patients. After 3 to 10 months (median, 8 months) postoperatively, no relapse has been observed. Conclusions Our data emphasize laparoscopic fenestration as the treatment of choice for children with posttransplant lymphoceles, because it is safe, effective, and technically easy to perform. If done early after diagnosis, renal function will recover immediately.