Abstract: Objective: To describe relationships between use of the Personal Patient Profile-Prostate (P3P) decision support system and patient characteristics, and perceived preparation for decision making (PrepDM), satisfaction and decisional regret in the context of prostate cancer treatment choice.Methods: 494 men with localized prostate cancer (LPC) were randomized to receive the P3P intervention or usual care and completed pre-treatment, 1-month and 6-month outcome measures. Multivariable linear regression models were fit for each outcome.Results: Physician consult visits prior to enrollment, race/ethnicity, and use of clinic-provided books were significant predictors of perceived PrepDM at 1 month. Prior Internet use and PrepDM significantly predicted 6-month decision satisfaction. Decisional regret was significantly predicted by demographics, anxiety, PrepDM score, and EPIC bowel domain score at 6 months. Use of P3P did not predict any outcome.Conclusion: While the P3P intervention did not significantly affect the outcomes, pre-enrollment information and preparation were strong predictors of the 1- and 6-month outcomes. Decision regret was significantly influenced by personal characteristics and post-treatment symptoms/side effects.Practice implications: Information received and used between biopsy and the treatment options consult visit is likely to make a difference in decision satisfaction.