Dermatitis herpetiformis and gluten-sensitive enteropathy are diseases in which exposure to gluten results in an inflammatory response. Both diseases are associated with certain human lymphocyte antigen alleles, and gluten-sensitive enteropathy is well known to cluster in families. Gluten-sensitive enteropathy has also been reported in families of patients with dermatitis herpetiformis. Despite this evidence that dermatitis herpetiformis is a genetic disease, reports of the familial occurrence of dermatitis herpetiformis are rare. We have obtained family histories from 92 patients with dermatitis herpetiformis with 740 first-degree relatives. Six of these relatives have dermatitis herpetiformis. Comparison of these data with the expected prevalence of dermatitis herpetiformis shows this incidence to be highly significant (p less than 0.0001), strongly suggesting that dermatitis herpetiformis is a familial disease, presumably because of shared genetic factors but possibly because of a shared environment.