Continuous ambulatory peritoneal dialysis (CAPD) is frequently used in the pediatric age group for reversible and end-stage renal failure. Most pediatric patients tolerate this therapy with few complications. Approximately 2% of children, however, develop massive unilateral hydrothorax. This major complication usually results in the discontinuation of peritoneal dialysis in all forms and the institution of hemodialysis. Occult diaphragmatic defects account for most adult and pediatric patients who develop this complication. Three pediatric patients receiving CAPD complicated by massive hydrothorax are described. All patients were successfully treated by thoracotomy and repair of the diaphragmatic eventration with an immediate return to CAPD. This is the first report of successful therapy of this kind in children. A review of the cause, diagnosis, and treatment of massive hydrothorax developing during CAPD therapy is presented.