Background. Castleman's disease is a benign lymphoproliferative disorder. The disease may be localized or multicentric. Three histologic variants are recognized: hyaline vascular, plasma cell, and mixed types. Case. A 20-year-old man presented with large left axillary mass. The histologic examination of the resected mass showed follicular pattern with large nodules of mantle cells arranged concentrically around atrophic and vascularized germinal centers. There was also some benign-appearing bone trabeculae interspersed with lymphoid tissue. The diagnosis of Castleman's disease, hyaline-vascular type with osseous metaplasia, was made.