Seventy-eight patients with dermatitis herpetiformis have been followed up for periods ranging from 3 to 14 years (mean 7.4). Forty-two patients were treated with gluten-free diet (GFD) and thirty-six took a normal diet (ND). Thirty of the forty-two (71%) taking the GFD were able to discontinue drugs previously needed to control their rash compared with five (14%) of the thirty-six patients taking a ND. The mean time taken to reduce drug requirements for patients taking a GFD was 8 months (range 4-30), and for stopping drugs, 29 months (range 6-108). The incidence of macroscopic abnormality of the small intestine decreased from 69 to 15%, and the mean intra-epithelial lymphocyte count decreased significantly in those patients taking a GFD, whereas there was no significant change in patients taking a ND. The improvement in the skin and intestinal lesions was related to the strictness of the GFD.