We describe an unusual case involving an infected hepatic cyst. An 88-year-old woman presented with acute onset of right upper quadrant abdominal pain, mild left lower abdominal pain, diarrhea, and fever. On admission, computed tomography revealed multiple hepatic cysts including an 8-cm cyst located in the left medial segment of the liver, which demonstrated a thickened wall enhanced with contrast media. Ultrasonography showed an 8-cm hypoechoic lesion which differed in appearance from the other, anechoic hepatic cysts. The serum concentration of C-reactive protein was 29.8 mg/dL; white blood cell count, 12,800/microL; CA19-9, 96 U/mL; and CEA, 2.2 ng/mL. Diagnosis of infected hepatic cyst was made by percutaneous transhepatic drainage of the cyst. Milky fluid was obtained and the patient's right upper quadrant abdominal pain resolved after drainage. The cyst fluid CA19-9 concentration was 18,000 U/mL. Cytology of the cyst fluid was negative. Serum CA19-9 (41 U/mL) and CEA (1.8 ng/mL) concentrations were improved 1 week after drainage. Escherichia coli was cultured from the drainage fluid. The patient was discharged 27 days after admission. Percutaneous transhepatic drainage is effective in the treatment of infected hepatic cysts.