Objective: This randomized trial was conducted to assess the impact of a mediated decision support intervention on primary care patient prostate cancer screening knowledge, decisional conflict, informed decision making (IDM), and screening. Methods: Before a routine office visit, 313 male patients eligible for prostate cancer screening completed a baseline telephone survey and received a mailed brochure on prostate cancer screening. At the visit, participants were randomized to either an enhanced intervention (El) or a standard intervention (SI) group. Before meeting with their physician, El Group men had a nurse-led "decision counseling" session, while SI Group men completed a practice satisfaction survey. An endpoint survey was administered. Survey data, encounter audio-recordings, and chart audit data were used to assess study outcomes. Results: Knowledge increased in the El Group (mean difference of +0.8 on a 10-point scale, p = 0.001), but decisional conflict did not change (mean difference of -0.02 on a 4-point scale, p = 0.620). The El Group had higher IDM (rate ratio = 1.30, p = 0.029) and lower screening (odds ratio = 0.67, p = 0.102). Conclusion: Nurse-mediated decision counseling increased participant prostate cancer screening knowledge, and influenced informed decision making and screening. Practice implications: Nurses trained in decision counseling can facilitate shared decision making about screening. (C) 2010 Elsevier Ireland Ltd. All rights reserved.