BACKGROUND: There is limited evidence about how to ensure that patients are helped to make informed medical care decisions. OBJECTIVE: To test a decision support intervention for uterine fibroid treatments. DESIGN AND SETTING: Practical clinical trial to test informed choice assistance in 4 randomly assigned gynecology clinics compared to 5 others providing a pamphlet. PATIENTS: Three hundred women facing a treatment decision for fibroids over a 13-month period. INTERVENTION: Mailed DVD and brochure about fibroid treatments plus the Ottawa decision guide and an offer of counseling soon after an index visit. MEASUREMENTS: Mailed survey 6 to 8 weeks later asking about knowledge, preferences, and satisfaction with decision support. RESULTS: In total, 244 surveys were completed for an adjusted response rate of 85.4%. On a 5-point scale, intervention subjects reported more treatment options being mentioned (3.0 v. 2.4), had a higher knowledge score (3.3 v. 2.8), and were more likely to report being adequately informed (4.4 v. 4.0), and their decision was both more satisfactory (4.3 v. 4.0) and more consistent with their personal values (4.5 v. 4.2). Neither knowledge nor use of the intervention was associated with greater concordance between preferences and decisions. LIMITATIONS: Implementation of intervention may not have been well timed to the decision for some patients, limiting their use of the materials and counseling. CONCLUSION: It is difficult to integrate structured decision support consistently into practice. Decision support for benign uterine conditions showed effects on knowledge and satisfaction but not on concordance.