Lymphoceles occurred in 25 of 115 patients after renal transplantation in the Oxford Unit. Signs of obstruction or pressure were produced in 16 of these 25 patients (15%), while nine were detected on a routine ultrasound scan. The 16 symptomatic lymphoceles were treated successfully by aspiration or surgical fenestration into the peritoneal cavity . Of the possible causes examined, diathermy and division of iliac lymphatics seemed to be the most likely reason for this high incidence. Since a technique of ligating or clipping the iliac lymphatics has been adopted, no lymphoceles have occurred in the subsequent 70 transplants.