Migration of Ascaris lumbricoides into the gallbladder is rare, unlike ascariasis of the bile duct, and, when it does occur, treatment is generally by endoscopic or surgical extraction. We describe a case of the successful treatment of gallbladder ascariasis with conservative therapy. A 44-year-old Korean man was admitted because of nausea and right upper quadrant pain that did not respond to medical control and had worsened 1 day before admission. Abdominal ultrasonography showed a long, linear, moving echogenic structure in the distended lumen of the gallbladder, but no abnormal dilation of the bile duct. Computerized tomography showed a linear soft-tissue density in the dependent portion of the gallbladder. The patient presented with eosinophilia, and abnormal liver function results, but no fever or hepatomegaly. Based on these findings, and presuming a diagnosis of gallbladder ascariasis, we administered antiparasitic medication (albendazole 400 mg/day for 1 day). Seven days later, we obtained one adult female A. lumbricoides from the feces. The symptoms were fully resolved, and no moving structure could be visualized in the gallbladder by ultrasonography. We recommend that initial therapy for gallbladder ascariasis should involve conservative treatment, unless an associated disease is present or a complication arises.