Background: Controversy surrounds treatment for localized prostate cancer (LPC).Objectives: To assess men's localized prostate cancer (LPC) knowledge and its association with decision-making difficulty, satisfaction and regret.Methods: Population-based sample of 201 men (104 white, 97 black), < 75 years with newly diagnosed LPC completed a self-administered survey.Results: Mean age was 61(؎7.6) years; two-thirds had less than a Bachelor's degree. Mean LPC knowledge was low, 5.87 (؎2.53, maximum score 11). More than a third of men who received surgery or radiation did not know about serious long-term treatment side effects. Fewer than half of the men correctly answered comparative side effect and survival benefit questions between surgery and radiation. Knowledge gaps were greatest among black men, men with lower education, single men. Tumor aggressiveness (i.e. PSA level, Gleason score) and treatment choice were not associated with knowledge. Knowledge was not associated with decisional satisfaction or regret. However, greater knowledge was associated with greater decision-making difficulty (P ‫؍‬ .018).Conclusions: Significant LPC knowledge gaps existed across groups, with greater knowledge gaps among black men. The association of decision-making difficulty with knowledge was independent of race. Better patient education is needed, but may not alleviate men's decision-making difficulty due to inherent scientific uncertainty. (J Am Board Fam Med 2017;30:288 -297.)