Objectives: Diagnosis of unrecognized celiac disease is potentially important, The prevalence of celiac disease in patients with insulin-dependent diabetes mellitus is uncertain, We report the prevalence of celiac disease in a stratified random sample (n = 101) of adult insulin-dependent diabetic patients (age, 18-59 yr) attending our clinic, and in an age-and sex-matched control group (n = 51). Methods: Screening was by anti-endomysial antibody, measured by indirect immunofluorescence using sections of human umbilical cord, Results: Celiac disease had not been suspected in any patient at the time of screening, Eight patients tested positive for anti-endomysial antibody, all of whom had a distal duodenal biopsy performed, Five patients had histologic evidence of celiac disease, One patient with negative histology was receiving immunosuppressive therapy for a renal-pancreas transplant, Of the five patients with abnormal histology, two improved on gluten restriction, one was unable to comply, one refused treatment, and one was lost to follow-up, No control subject tested positive for endomysial antibody, Conclusions: Patients with insulin-dependent diabetes have an increased prevalence of celiac disease. Because most cases are clinically unrecognized consideration should be given to screening all insulin-dependent diabetes mellitus patients with endomysial antibodies.