Castleman's disease is a rare lymphoproliferative disorder with unknown underlying cause. Three histologic variants (hyaline-vascular, plasma cell and mixed) as well as 2 clinical groups (localized and multicentic) have been described. Most patients with the hyaline-vascular variant are asymptomatic other than localized pressure from the mass. Hyaline-vascular Castleman's disease was commonly found as intrathoracic presentation. Extrathoracic lesions have been reported in the retroperitoneum, mesentery, central nervous system, orbit, pelvis, neck, axilla, and skeletal muscles. Herein, we report a case of hyaline-vascular Castleman's disease mimicking a gastric submucosal leiomyoma that has rarely been reported in English literature review. The lesion was not actually developing from the stomach, however, the clinical presentation was mimicking a submucosal gastric tumor. Furthermore, the patient in this case had both chronic hepatitis C and splenosis. The relationship between the underlying diseases and the development of the CD deserves further investigations.