Dermatitis herpetiformis (DH) is an external manifestation of coeliac disease presenting with blistering rash and pathognomonic cutaneous IgA deposits. Better knowledge of subclinical forms and serological testing has resulted in a sharp increase in the incidence and prevalence of coeliac disease. To investigate the prevalence of DH and analyse whether the incidence of DH changed when the occurrence of coeliac disease increased. All 477 patients with DH diagnosed from 1970 onwards at the Tampere University Hospital were analysed for prevalence in 2009. The incidence of DH was calculated in three 10-year periods from the year 1980. The prevalence of DH was 75·3 per 100,000 which is eight times lower than the prevalence of coeliac disease in our area. The annual incidence of DH in the whole period was 3·5 per 100,000, and in the three 10-year periods 5·2, 2·9 and 2·7 per 100,000, respectively. The decrease in incidence between the first and second 10-year period was significant (P<0·001). The male to female ratio of DH was 1·1:1. The mean age at diagnosis increased significantly during the study, in men from 35·3 to 51·1 years and in women from 36·3 to 45·8 years. The present study shows the highest prevalence of DH reported to date. Although the overall incidence of DH was also high, a significant decrease occurred in the 1990s, which is in contrast to the incidence of coeliac disease. © 2011 The Authors. BJD © 2011 British Association of Dermatologists 2011.