Background/Aims: Disaccharidase assay is used for assessing carbohydrate intolerance in children, but its usefulness in adults is not known. The aim of this study is to assess the prevalence of disaccharidase deficiency in patients with unexplained gastrointestinal symptoms. Methods: A retrospective review of adults with chronic (> 1 year) abdominal symptoms and negative imaging and endoscopy/colonoscopy and who completed bowel symptom questionnaire and duodenal biopsy for lactase, maltase, sucrase, and palatinase was performed. A subset also underwent 25 g lactose breath test (LBT). Results: One hundred twenty patients (females = 83) were evaluated, of whom 48 also underwent LBT. Fifty-six (46.7%) patients had enzyme deficiency; 44 (36.7%) had single (either lactase or maltase), 1 had 3 enzyme deficiencies, 11 (9.2 %) had all 4 disaccharidase enzyme (pan-disaccharidase) deficiency, and 64 (53.0%) had normal enzyme levels. Baseline prevalence and severity of 11 gastrointestinal symptoms were similar between normal and single enzyme deficiency groups. The sensitivity and specificity of LBT was 78.3% and 72.0%, respectively and overall agreement with lactase deficiency was 75.0%. Conclusions Isolated disaccharidase deficiency occurs in adults, usually lactase and rarely maltase, and pan-disaccharidase deficiency is rare. Baseline symptoms or its severity did not predict enzyme deficiency.