BACKGROUND Dermatitis herpetiformis (DH) is an extra-intestinal manifestation of coeliac disease and most patients adhere to a life-long gluten free diet (GFD). Increased mortality rates have been reported in coeliac disease but knowledge in DH is scanty. OBJECTIVES To survey the mortality rate and causes of death in a large cohort of patients with DH. MATERIAL AND METHODS Patients with DH (n = 476 consecutive patients) diagnosed from 1970 onwards at the Tampere University Hospital were analysed for causes of death during 1971-2010. A questionnaire survey on key aspects of health behaviour was performed in patients with DH and comparisons were made with the Finnish population. RESULTS The total number of deaths during 9079 person years followed up was 77 whereas 110 were expected. The standardized mortality rate (SMR) for all causes of death was significantly reduced, being 0·70 (95% CI 0·55-0·87), and similar in both sexes. The SMR was equal in the patients with DH with (0·73) and without (0·77) small bowel villous atrophy. The SMR was significantly reduced (0·38) for deaths due to cerebrovascular diseases. The SMR due to lymphoproliferative malignancies was significantly increased (6·86) in the first 5 years of follow-up but not thereafter. The questionnaire survey documented that 97·7% of the patients with DH adhered to a GFD. The patients reported significantly less hypercholesterolaemia and there were fewer current and past smokers compared with the age- and sex-matched control population. CONCLUSIONS The present long-term follow-up study of DH documented significantly reduced all-cause and cerebrovascular disease mortality. Strict adherence to a GFD, less smoking and hypercholesterolaemia may play a role in the observed health benefit.