Abstract Purpose A substantial proportion of men with localized prostate cancer (lPCa) later regret their treatment decision. We aimed to identify factors contributing to decisional regret. Methods We conducted a longitudinal study, in which men with lPCa were surveyed at four measurement points: T0 (baseline) = prior to treatment; T1 = 6; T2 = 12; T3 = 18 months after baseline. χ2-tests and independent t-tests were used to compare men undergoing different treatments [Active Surveillance (AS) vs. local treatment]. Logistic regression models were fitted to investigate the associations between predictors (time pressure, information provided by the urologist, impairment of erectile functioning, satisfaction with sexual life) and the criterion decisional regret. Results At baseline, the sample included N = 176 men (AS: n = 100; local treatment: n = 76). At T2 and T3, men after local therapies reported higher regret than men under AS. Decisional regret at T3 was predicted by time pressure at baseline (OR 2.28; CI 1.04–4.99; p < 0.05), erectile dysfunction at T2 and T3 (OR 3.40; CI 1.56–7.42; p < 0.01), and satisfaction with sexual life at T1–T3 (OR 0.44; CI 0.20–0.96; p < 0.05). Conclusions Time pressure, erectile dysfunction, and satisfaction with sexual life predict decisional regret in men with lPCa. Mitigating time pressure and realistic expectations concerning treatment side effects may help to prevent decisional regret in PCa survivors. Trial registration number DRKS00009510; date of registration: 2015/10/28.