An unusual case involving an infected hepatic cyst in which the correct diagnosis was made without operation is reported. A 93-year-old woman presented with acute onset of right upper quadrant abdominal pain, mild left lower quadrant abdominal pain, diarrhea, and fever. On admission, computed tomography revealed a 15 cm solitary hepatic cyst in the anterior-superior segment of the liver with a thickened wall that enhanced with contrast media. Ultrasonography demonstrated a 15 cm anechoic lesion with a hypoechoic area in the dependent portion of the cyst and a thickened wall. The serum concentration of C-reactive protein was 24.3 mg/dL, and the white blood cell count was 13,800/microL. A diagnosis of infected hepatic cyst was suspected, and percutaneous transhepatic drainage of the cyst was performed. Milky yellow fluid was obtained and the patient's right upper quadrant abdominal pain resolved after drainage. Klebsiella pneumoniae was cultured from the drainage fluid. The patient was discharged 20 days after drainage. Infection has not recurred and the hepatic cyst has not enlarged after 18 months.