"Sweet" hydrothorax (SH) is a complication in patients with peritoneal dialysis. Increase in intra-abdominal pressure because of flow of peritoneal fluid and its permanence can produce fluid effusion through the pleuroperitoneal communication, leading to hydrothorax. The incidence reported in the literature varies between 1.6% and 6% occurring at any time during peritoneal dialysis follow-up, with more frequent involvement of right hemithorax. We report the case of a patient with SH confirmed with the biochemical analysis of the pleural fluid given the clinical and radiological suspicion, deciding the definitive switch to hemodialysis.