We screened for celiac disease, by means of IgA class anti-endomysium antibodies (EmA), 383 consecutive adults with insulin-dependent diabetes mellitus (IDDM). Two control populations entered the study as well: 151 adults with biopsy proven celiac disease, as true positives; and 520 controls (healthy and diseased) as true negatives. IgA-EmA positivity was found in 145 of 151 (96%) celiac disease patients but in none of the controls (100% specificity). EmA were positive in 12 of 383 (3.13%) IDDM patients: 10 of these positives underwent intestinal biopsy, which showed either partial or total villous atrophy. Only one patient presented with gastrointestinal complaints, but severe iron deficiency was found in all. The IDDM celiac patients were started on a gluten-free diet: four refused both the diet and the follow-up protocol. Approximately one year after gluten withdrawal no significant change in the degree of diabetes control was observed, while an increased requirement for insulin was observed in three of four patients who strictly complied with the diet. The prevalence of biopsy-proven celiac disease among adult IDDM patients (1:38), eight times higher than that recently estimated for the general Italian population and the absence, except in one case, of gastrointestinal symptoms emphasizes the benefit of screening programs on populations at risk.