A high frequency of celiac disease is reported in patients with collagenous colitis. Limited information is available on the frequency of celiac disease in lymphocytic colitis. The aim of our study was to determine the prevalence of celiac disease in microscopic colitis (collagenous and lymphocytic colitis). Patients were identified from a pathology registry of microscopic colitis from 1987 to 1999. Pathology reports and medical records were reviewed for previous small bowel biopsies and/or celiac serology. We identified 113 patients with microscopic colitis, and 46 patients underwent a small bowel biopsy and/or celiac serology. Of these, 27 patients had lymphocytic colitis (63% female; age, 58.6 ± 16.2 years) and 19 patients had collagenous colitis (79% female; age, 61.8 ± 13.6 years). Small bowel biopsy alone was performed in 28 of 46 patients, celiac serology alone was performed in 10, and both small bowel biopsy and celiac serology were performed in 8. Celiac disease was identified in 4 patients by small bowel histology; all had lymphocytic colitis (4 of 27 patients, 15%). This frequency of celiac disease is significantly higher than the highest reported U.S. prevalence of celiac disease (4/1,000 individuals;p < 0.01). There is a high frequency of celiac disease in patients with lymphocytic colitis. Given the importance of the early detection of celiac disease, it should be excluded in all patients with lymphocytic colitis, particularly if diarrhea does not respond to conventional treatment.