BACKGROUND: Little is known about compliance with colonoscopy as a screening method in first-degree relatives of patients with large adenomas. Aims To evaluate the compliance with screening colonoscopy among this population, and its determinants. METHODS: Data were obtained from the family part of the GEADE study, a study on genetic factors of colorectal adenomas. Index cases were 306 patients with adenomas > or = 10 mm. All living first-degree relatives aged 40-75 who could be contacted by the index case were asked to undergo a colonoscopy, unless they had had one in the previous 5 years. RESULTS: Among 674 eligible relatives, 56 had had a colonoscopy within the preceding 5 years and 114 underwent a screening colonoscopy resulting in a compliance with screening colonoscopy of 18%. This was not related to most characteristics of index cases. Compliance was significantly lower when the index case lived in the Greater Paris area than when he/she lived in other areas (12% vs. 21%). It was higher in siblings (18%) and offspring (23%) than in parents (9%) and in relatives under 55 years old (22%) than in relatives aged 55 and over (15%). CONCLUSIONS: Compliance with colonoscopy was low in first-degree relatives of patients with large adenomas. The reasons for this should be determined and appropriate strategies developed to increase compliance.