BACKGROUND To report a rare case of spontaneous rupture of an infected renal cyst into the peritoneal cavity. METHODS We report a case of 66-year old man with autosomal dominant polycystic kidney disease and kidney dialysis who had suffered from intestinal obstruction and peritoneal syndrome for 2 days associated with purulent urine. An exploratory laparotomy found multiple hepatic cysts and bilaterally enlarged polycystic kidneys. We noted left renal cyst infected and ruptured into the peritoneal cavity causing general peritonitis. The patient died from septic shock and hemodynamic failure. CONCLUSIONS The peritoneal rupture of infected renal cyst is an exceptional and serious complication of polycystic kidney disease. Medical and surgical treatments are urgent to prevent lethal complications.