A 29-year-old female presented with upper abdominal pain. An upper gastrointestinal radiograph and endoscopy revealed an extra compression in the lesser curvature of the body of the stomach. A computed tomography scan and magnetic resonance imaging revealed a tumor located between the left lobe of the liver and the lesser omentum of the stomach. F-18 fluorodeoxyglucose positron emission tomography revealed high uptake at the tumor in the upper abdomen. In an angiogram, a large hypervascular mass had a prominent vascular supply from the left gastric artery; venous pooling and an enlarged feeding vessel were also apparent. From these results, we suspected that the patient had Castleman's disease arising from the lesser omentum. The patient underwent hand-assisted laparoscopic tumor resection. The resected tumor was an encapsulated mass, the surface of which was smooth and the dimensions of which were 77 x 51 x 43 mm. Based on microscopic findings, we diagnosed hyaline vascular type Castleman's disease. Since surgical intervention, the patient has remained asymptomatic, with no pathologic clinical or laboratory findings. Castleman's disease that occurs in the lesser omentum is extremely rare, and the preoperative diagnosis is very difficult. For the localized type of Castleman's disease, clinical findings are usually improved by complete surgical resection.