We have studied the occurrence of associated diseases in a cohort of 305 patients with dermatitis herpetiformis (DH) followed up for a mean of 10 years. The results were compared with those from 383 patients with coeliac disease (CD). Twenty‐nine (9.5%) patients with DH and 73 (19.1%) with CD had concomitant endocrine or connective tissue disorders. The following associations were found: autoimmune thyroid disease (4.3% of DH patients and 6.0% of CD patients), insulin dependent diabetes (1.0% DH and 5.5% CD), lupus erythematosus (1.3% DH and 0.3% CD), Sjögren's syndrome (1.0% DH and 2.9% CD), sarcoidosis (1.3% DH and 1.8% CD), and vitiligo or alopecia areata (1.6% DH and 0% CD). We have shown that patients with DH are similar to those with CD in that many have associated endocrine or connective tissue disorders. Most of these diseases began before DH had been diagnosed suggesting that those on a gluten‐free diet are not at special risk of contracting them.