The diagnosis of irritable bowel syndrome (IBS) is based on symptom assessment such as the Rome III criteria. It is sometimes difficult to clinically distinguish IBS from adult-onset celiac disease (CD). Individuals with CD presenting with relatively vague abdominal symptoms are at risk of been dismissed as having IBS. This study aimed to investigate the prevalence of patients with CD among those that fulfill the Rome III criteria for IBS from among patients referred to the gastroenterology section of our hospital over the last 5 years. The study included a total of 968 patients with an average age of 32 years (range 18-59 years). Females constituted 95% of all patients. Duodenal biopsies were obtained during standard gastroscopy. Sections from these biopsies were stained with haematoxylin and eosin and immunostained for human leucocytes CD45 using the avidin-biotin complex (ABC) method. The sections were then histopathologically examined. Four patients had CD: one with Marsh type 3b, and 3 with Marsh type 1. All four of these patients were positive for tissue transglutminase antibodies (anti-t-TG) IgA and were females aged 24, 20, 36 and 38 years. These 4 patients fulfilled the Rome III criteria for the sub-type IBS-diarrhea. This amounts to a prevalence of 0.4% of CD in IBS patients. The present findings support the notion that IBS patients should be routinely examined for CD. This applies to all subtypes of IBS.