Objective: Prostate cancer (PCa) patients often must decide between several treatment modalities considered equally efficacious, but associated with different benefits and side-effects. For some, the decision-making process can be difficult, but little is known about patient characteristics and cognitive processes that might influence the difficulty of such decisions. This study investigated the roles of dispositional optimism and self-efficacy in PCa treatment decision-making difficulty and satisfaction. Methods: One hundred and twenty-five patients with clinically localized PCa completed a mail-in paper-and-pencil survey after they had made their treatment decision, but prior to treatment. Results: After adjusting for covariates, optimism and treatment decision-making self-efficacy were associated with less difficulty and greater satisfaction with the treatment decision-making process. Effects of optimism on difficulty and satisfaction were partially mediated by self-efficacy for making the treatment decision. Conclusions: Men with PCa and who are low in optimism may be at greater risk for treatment decision-making difficulty and lack of treatment decision-making satisfaction, in part, because they have lower confidence in their ability to make the decision compared with those who are more optimistic. As self-efficacy perceptions are modifiable, consideration should be given to including self-efficacy enhancing components as part of PCa treatment decision-making interventions. Copyright © 2008 John Wiley & Sons, Ltd.