Patients with insulin-dependent diabetes mellitus, autoimmune thyroid disease, Addison's disease, and alopecia areata are at increased risk of celiac disease. We investigated whether patients with more than one autoimmune endocrinologic disorder are even more susceptible to celiac disease or have celiac-type mucosal inflammation. All 62 patients found to have such multiple diseases in 1994-1996 were investigated. Small bowel biopsy was performed on all voluntary nonceliac subjects. The villous structure and density of intraepithelial lymphocytes were examined, and HLA-DQ alleles were determined. Seven (11%) patients had celiac disease: six cases were detected earlier and there was one new case; in addition, two had minor villous deterioration and five an increased density of mucosal intraepithelial gammadelta+ T-cells. HLA-DQ2 or DQ8 alleles were found in all subjects with mucosal changes. Patients with multiple autoimmune disorders clearly run an increased risk of developing celiac disease, and some of them have minor mucosal changes compatible with the early signs of the disease.