Simple renal cysts are most commonly found in the elderly, male population. The majority of simple renal cysts remain untreated, except on the rare occasion when they become complicated with hemorrhage, infection or rupture. We present the case of a 31-year-old female with a simple renal cyst which was initially treated as acute pyelonephritis. A high clinical suspicion led to the diagnosis of an infected renal cyst which was treated with antibiotic therapy and radiological drainage. There were minimal complications and the patient made an uneventful recovery.