Purpose: To assess the normal small bowel parameters, namely bowel diameter, bowel wall thickness, number of folds (valvulae connivientes) per 2.5 cm (in.), fold thickness and interfold distance per small bowel segment (duodenum, jejunum, proximal ileum, distal ileum and terminal ileum) on MR enterography.Materials and methods: Between September 2003 and January 2008, 280 MR enterography examinations were performed for investigation of known or suspected mall bowel pathology. 120 of these examinations were normal. Sixty-five (m = 29, f = 36, mean age = 34 years, range = 17-73 years) of 120 examinations without a prior small bowel diagnosis, with no prior or subsequent abnormal radiology or endoscopy examinations, no prior small bowel surgery and with a minimum 3 years follow-up demonstrating normality were retrospectively evaluated for the described small bowel parameters.Results: We found the mean diameter of the duodenum to be 24.8 mm (S.D. = 4.5 mm), jejunum to be 24.5 mm (S.D. = 4.2 mm), proximal ileum to be 19.5 mm (S.D. = 3.6 mm), distal ileum to be 18.9 mm (S.D. = 4.2mm) and terminal ileum to be 18.7 mm (S.D. = 3.6 mm). The number of folds per 2.5 cm varied from 4.6 in the jejunum to 1.5 in the terminal ileum. The fold thickness varied from 2.1 mm in the duodenum to 1.8 mm in the terminal ileum. The small bowel parameters gradually decreased in size from the duodenum to the smallest measurements which were in the terminal ileum. The bowel wall is similar in size throughout the small bowel measuring 1.5 + 0.5 mm.Conclusion: These results provide the mean, range of normality and standard deviation of the small bowel parameters per segment on the current population on MR enterography. From our experience, knowledge of these parameters is extremely helpful and essential in the everyday assessment of MR enterography studies. (C) 2009 Elsevier Ireland Ltd. All rights reserved.