Peritoneal dialysis (PD) confers many advantages, including a better quality of life for children with end-stage renal disease; however, the procedure is associated with several complications, including pleuroperitoneal leaks. Here, we report an unusual case of hydrothorax caused by long-term PD in a child, which was further complicated by pneumonia. A 9-year-old boy who had received CAPD for 22 months presented with dyspnea, swelling, and increased body weight. Chest tube drainage yielded 500 mL of transudative fluid. Computed tomography peritoneography revealed increased outflow from the peritoneum to the pleural cavity. PD was suspended, and hemodialysis (HD) was initiated. Video-assisted thoracoscopic surgery was performed; however, because the patient had pneumonia during hospitalization, pleural adhesions with a septated appearance occurred. This resulted in difficulties identifying pleuroperitoneal fistula (PPF). Right pleural effusion resolved following pleurodesis using bleomycin. Regular HD was performed for 10 weeks, and PD was subsequently reinitiated. There was no recurrence of hydrothorax during long-term follow-up. We suspect that the underlying mechanism of hydrothorax in our patient was associated with a PPF that formed either due to a congenital diaphragmatic defect or an acquired defect, resulting in dialysate leakage. Our case demonstrates that a temporary switch from PD to HD, accompanied by pleurodesis, may help resolve hydrothorax that occurs as a complication of long-term PD.