Postoperative delirium is one of the most spectacular, frightening and misdiagnosed postoperative complications of surgery. We describe the case of a caucasian 77-year-old male patient, who developed a severe postoperative delirium after combined transurethral resection of the prostate and cystolithotripsy. This systemic and unpredictable complication of endoscopic surgery is caused by excessive absorption of electrolyte-free irrigation fluids, leading to brain edema and metabolic encephalopathy. The clinical spectrum ranges from asymptomatic hyponatraemia, to electrocardiographic (ECG) changes, nausea, vomiting, convulsions, coma, pulmonary edema, cardiovascular compromise and death. Because of the heterogeneous clinical presentation diagnosis can be difficult. In a patient who develops alterations of consciousness with evidence of hypervolemia and hyponatremia after endoscopic surgery, transurethral resection syndrome must be considered.