Abstract Sweat gland abnormalities occur much more frequently than hitherto described in cutaneous graft versus host disease (GVHD). Two patterns of abnormalities were identified in 80 per cent of cases of acute GVHD: a cytopathic pattern consisting of a combination of basal vacuolopathy with or without lymphocytic infiltration and basal cell degeneration, and a proliferative pattern consisting of basal cell hyperplasia. In chronic GVHD, complete sweat gland destruction with fibrosis was commonly observed. Squamous metaplasia and dilatation of the sweat glands were less frequently identified. Ki67 immunostaining confirmed proliferative activity in the basal cells of the distal duct. HLA‐DR antigens were expressed on the basal cells of the duct and secretory glands in acute GVHD but not in normal skin. Langerhans cells were absent in both normal and abnormal sweat glands. The role of HLA‐DR or Langerhans cells in the initiation of GVHD is questioned in the light of the new data and the primary involvement of proliferating cells is confirmed.