Hydrothorax in a patient treated with peritoneal dialysis (PD) poses a diagnostic dilemma. Hydrothorax due to migration of dialysis fluid across the diaphragm and into the pleural space creates a serious complication of PD but generally does not threaten life. Shortness of breath causes the patient to seek medical attention. A sudden diminution in dialysis adequacy or poor ultrafiltration rate constitutes a unique marker for patients treated with PD compared to the general population. This article reviews the etiology for hydrothorax specifically in the PD population. Thoracentesis with chemical analysis of the fluid, imaging studies with and without contrast or markers, and video-assisted thoracoscopic surgery play important roles in the evaluation of hydrothorax. A conservative PD regimen, surgical intervention, and pleurodesis provide treatment options to those receiving PD.