Simple hepatic cysts are common benign lesions that are usually asymptomatic and require no treatment. However, complications can occur. This report describes a patient with an infected hepatic cyst treated with percutaneous transhepatic drainage. A 64-year-old woman presented at a nearby hospital because of acute right-upper-quadrant pain, mild left-lower-quadrant pain, diarrhea, and fever. She was admitted and received intravenous antibiotics for 1 week, but symptoms persisted. She was, therefore, referred to our hospital. On admission, ultrasonography demonstrated multiple hepatic cysts. One 13-cm lesion was hypoechoic, unlike the other simple cysts, which were anechoic. Computed tomography showed that the density of the hypoechoic cyst was slightly higher than that of the other cysts. The wall of the cyst was thickened and showed contrast enhancement. On initial laboratory tests the serum C-reactive protein concentration was 18.49 mg/dL, and the white-cell count was 13,300/microL. An infected hepatic cyst was suspected, and percutaneous transhepatic drainage of the cyst was performed. A catheter was inserted into the cyst, and dark red fluid was obtained. The right-upper-quadrant pain gradually resolved after drainage. An infected hepatic cyst was diagnosed, and system antibiotics were administered. However, the mild left-lower-quadrant pain persisted. No pathogens were isolated from the drainage fluid. Minocycline hydrochloride (200 mg) was injected, and the catheter was clamped for 30 minutes, once daily for 3 days. The serum C-reactive protein concentration was 1.78 mg/dL, and the white-cell count was 5,700/microL. The left-lower-quadrant pain resolved, and colonoscopic examination revealed multiple diverticula of the sigmoid colon. Infection has not recurred, and the hepatic cyst has not become larger.