We describe a long term study of 76 patients with dermatitis herpetiformis. Unlike patients with coeliac disease, where the peak incidence was during the first and fourth decades, no dermatitis herpetiformis patients presented in the first decade; also, there was a male preponderance in dermatitis herpetiformis which contrasts with the excess of females in coeliac disease. The apparent prevalence of dermatitis herpetiformis was 11 per 100 000 in our population; approximately one fifth of that of coeliac disease. Jejunal villous atrophy was present in 78% of our dermatitis herpetiformis patients, and a single jejunal biopsy was as effective at detecting this as the multiple biopsy technique. A majority of patients were able to stop, or radically reduce their dapsone or sulphapyridine treatment after the institution of a gluten free diet. Spontaneous remission of the skin lesion occurred in only two patients not receiving a gluten free diet. Gastric parietal or thyroid antibodies were detected in 38% of patients, and three cases of thyroid disease and two cases of pernicious anaemia were detected. Lymphoma developed in two patients, one being intestinal in origin. We conclude that a gluten free diet is of therapeutic benefit in dermatitis herpetiformis and that spontaneous remission is uncommon in those not on a diet. Despite patchiness of the enteropathy, a single jejunal biopsy is quite adequate to diagnose the presence of upper intestinal villous atrophy.