['A cross-sectional age- and sex-matched study comparing the prevalence and size of dural ectasia in two groups of patients with Marfan syndrome. Group I comprised patients with moderate to severe back pain and Group II comprised patients without back pain.', 'To determine whether the presence and size of dural ectasia is associated with back pain in patients with Marfan syndrome.', 'Dural ectasia is present in more than 60% of patients with Marfan syndrome. Moderate to severe back pain is present in more than 50% of patients with Marfan syndrome. Most cases of significant low back pain in patients with Marfan syndrome do not have a clear cause. It would be useful for the clinician to know whether dural ectasia may be a cause of back pain in patients with Marfan syndrome with no other source.', 'Thirty two volunteers aged 30-50 with Marfan syndrome were enrolled as age- and sex-matched pairs with significant back pain (Group I) and without back pain (Group II). A completed questionnaire, physical examination, and magnetic resonance image of the lumbosacral spine were obtained. Dural volume caudal to L5 was calculated from the magnetic resonance data by specially designed software.', 'Dural ectasia was present in 76% of the patients in Group I, and 41% of the patients in Group II. The proportion of patients with dural ectasia was significantly higher in Group I. Furthermore, the mean dural volume was significantly higher in Group I, and a significant correlation between dural volume and Oswestry pain score was noted.'] Is dural ectasia associated with back pain in Marfan syndrome?