Approximately 20% of the 100,000 patients in the United States currently undergoing dialysis therapy for end-stage renal disease use the technique of peritoneal dialysis. We present a patient on peritoneal dialysis who developed a large posterior mediastinal mass, which on surgical exploration was found to be a paraesophageal hernia sac filled with omentum and dialysis fluid. We use this case as an introduction to review the thoracic complications of peritoneal dialysis.