Graft-versus-host disease (GVHD) is a life threatening complication that may occur following allogenic bone marrow transplantation (BMT) in the patients with aplastic anemia, leukemia or genetic immunodeficiency. It has been known that GVHD occurs approximately 70% of recipients of BMT in western countries but no definite incidence has been reported in Korea. In our St. Mary's Hospital, GVHD occurs in about 30% of BMT recipients. Histopathologically the acute phase skin shows diffuse lymphocytic infiltrates in the upper dermis with extensive exocytosis. Scattered throughout the epidermis are many degenerated keratinocytes, which are often associated with one or more satellite lymphocytes (satellite cell necrosis). In the chronic phase, acanthosis, eosinophilic keratinocytes resembling colloid bodies and mononuclear cell infiltrates in the upper dermis are noted. We reviewed 5 cases of acute GVHD and 6 cases of chronic GVHD. All patients received allogenic BMT from Jan. 1, 1992 to July 1, 1993. Ten patients were male and one was female. The mean age was 34 (20-70). The pathologic diagnosis was 3 cases of CML, 2 of ALL, 2 of AML (FAB M2), 2 of aplastic anemia, 1 of CLL and 1 of AML (FAB M5). The interval from BMT to GVHD varied from 14 days to 4 years (median 220 days). The skin and GI tract were involved in all eleven cases. Ten cases were histologically proven by skin biopsies, and two cases by salivary gland and colonic biopsies, respectively. The histological findings of the skin, salivary gland and colonic biopsieds were described. Immunohistochemical stain of the skin was done using CD4, CD8, HLA DR and Leu 7 antibodies.