The use of complementary and alternative medicine (CAM) is common in patients with inflammatory bowel disease (IBD). To determine the factors associated with use of CAM, the reasons commonly cited for use or nonuse of CAM, and the correlations between the factors associated with use of CAM and reasons for CAM use. The study included 2828 members of the Crohn's and Colitis Foundation of Canada. Subjects were mailed a questionnaire that included items on demographic characteristics, disease and treatment history, health attitudes and behaviours, and reasons for use or nonuse of CAM. Logistical regression was used to determine significant associations with current CAM use. In patients with Crohn's disease and ulcerative colitis, CAM use was associated with more severe disease activity, use of CAM for other purposes, use of exercise and prayer for IBD, and a desire for an active role in treatment decisions. CAM use was also associated with younger age in those with Crohn's disease, and less confidence in their IBD physician in those with ulcerative colitis. The most common reasons for CAM use were a desire for greater control, having heard or read that CAM might help, and the emphasis CAM places on treating the whole person. The most common reasons for not using CAM were that conventional treatments were successful, that not enough was known about CAM and a belief that CAM would not help. Disease activity and health attitudes and behaviours, but not demographic characteristics, are associated with CAM use by those with IBD.