Pleural effusions are a common finding in patients admitted on the medical take. This case decribes a patient using peritoneal dialysis who presented with progressive dyspnoea. Clinical examination and chest x-ray confirmed the presence of a pleural effusion. Thoracocentesis confirmed a 'sweet' effusion (higher pleural: serum glucose content), suggesting a pleuro-peritoneal leak. Optimal management involved switch from peritoneal to haemodialysis and referral to a specialised renal unit. This case highlights the need to consider the diagnosis of pleuro-peritoneal leak in patients using peritoneal dialysis who present to the acute medical unit with pleural effusion.