Background/Aims: Acquired lactase deficiency is a common cause of gastrointestinal symptoms but its etiology remains unclear. Celiac disease could lead to lactase deficiency and is much more common than previously suspected. Several studies have highlighted the prevalence of lactose intolerance in celiac disease, but studies assessing the prevalence of celiac disease in lactose intolerance are lacking. We evaluated the prevalence of celiac disease in patients with a positive H2-lactose breath test compared to a control group. Methods: This retrospective study included 54 patients (15 males/39 females; mean age 37.8 ±7 years) from southern Italy, referred to the Gastroenterology Unit for bloating and diarrhea after the introduction of milk or dietary lactose. They had a positive H2-lactose breath test and a negativeH2-glucose breath test. 50 blood donors were drawn from a similar population,matched for sex and age,and enrolled as a control group. All patients were screened for possible celiac disease by measuring the serum level of IgA antibodies to endomysium, anti-transglutaminase and total IgA. Patients positive for at least one of these markers were submitted to upper gastrointestinal endoscopy. Results: None of the patients had a IgA deficiency. 24%of the patients showed positivity of celiac disease antibodies compared to 2%in the control group (p < 0.001). Histologic samples of these patients showed villous atrophy (53.8%Marsh type IIIa, 38.4%Marsh IIIb, and 7.6%with Marsh type IIIc) confirming the celiac disease, while in the control subjects duodenal biopsies were normal. Conclusions: A high prevalence of celiac disease was observed in patients with a positive H2-lactose breath test compared to healthy controls. In these subjects lactase deficiency seems to be the only manifestation of celiac disease. We suggest serologic screening for celiac disease in all patients with a positive H2-lactose breath test before beginning a milk-exclusion diet. Background / Aims: Acquired lactase deficiency is a common cause of gastrointestinal symptoms but its etiology remains unclear. Several studies have highlighted the prevalence of lactose intolerance in celiac disease, but studies assessing the prevalence of celiac disease in lactose intolerance are lacking. We evaluated the prevalence of celiac disease in patients with a positive H2-lactose breath test compared to a control group. Methods: This retrospective study included 54 patients (15 males / 39 females ; mean age 37.8 ± 7 years) from southern Italy, referred to the Gastroenterology Unit for bloating and diarrhea after the introduction of milk or dietary lactose. They had a positive H2-lactose breath test and a negative H2-glucose breath test. 50 blood donors were drawn from a similar population, matched for sex and age, and enrolled as a control group. All patients were screened for possible celiac disease by measuring the serum level of IgA antibodies to endomysium, anti-transglutaminase and total IgA. patients positive for at least one of these markers were submitted to upper gastrointestinal endoscopy. Results: None of the patients had a IgA deficiency. 24% of the patients showed positivity of celiac disease antibodies compared to 2% in the control group (p <0.001). Histologic samples of these patients showed villous atrophy (53.8% Marsh type IIIa, 38.4% Marsh IIIb, and 7.6% with Marsh type IIIc) confirming the celiac disease, while in the control subjects duodenal biopsies were normal. Conclusions: A high prevalence of celiac disease was observed in patients with a positive H2-lactose breath test compared to healthy controls. manifestation of celiac disease. We suggest serologic screening for celiac disease in all patients with a positive H2-lactose breath test before beginning a milk-exclusion diet.