Background: The Personal Patient Profile-Prostate (P3P) is an Internet-based decision support program for men with newly diagnosed prostate cancer (CaP), which significantly reduced decisional conflict in treatment selection in a multicenter trial (2007 to 2009). We performed an ad hoc analysis of data from the trial (including five sites in Washington, Pennsylvania, Georgia, and Texas) to determine factors associated with initial treatment selection (watchful waiting [WW], external radiation [XRT], brachytherapy, or surgery [RP]) in men with localized CaP. Methods: Baseline patient characteristics measured for 462 patients included age, income (less than $35,000 vs. more than $35,000), employment (working vs. not ), relationship status (married/partnered vs. not), state and trait anxiety, amount of confidence in a particular physician (a lot vs. less), and whether the patient was seen by a urologist only or both a urologist and radiation oncologist. Univariate and multivariable logistic regression were used to identify predictors of initial treatment choice within 6 months of diagnosis. Results: Common treatment choices were RP (48%), XRT (21%), and WW (15%). In both univariate and multivariable analyses, men seen by a urologist only were more likely to choose WW (p=0.03 and p=0.02, respectively); employed men were less likely to choose WW (p=0.01 and p=0.02, respectively). In multivariable analysis, married/partnered men were more likely to choose surgery (p=0.03); anxiety was not statistically significantly associated with any treatment choice. Conclusions: Our findings suggest that treatment choice is related to social infrastructure and type of specialist seen. These findings should guide counseling of patients with newly diagnosed localized CaP. Further studies related to the role of sociodemographic characteristics and access to specialty care in initial treatment choice are warranted.