Prostate cancer (PC) mortality is the most valid end-point in screening trials, but could be influenced by the choice of initial treatment if treatment has an effect on mortality. In this study, PC treatment was compared between the screening and control arms in a screening trial. Data were collected from the European Randomized Study of Screening for Prostate Cancer (ERSPC). The characteristics and initial treatment of PC cases detected in the screening and the control arm were compared. Polytomous logistic regression analysis was used to assess the influence of study arm on treatment, adjusting for potential confounders and with statistical imputation of missing values. A total of 8,389 PC cases were detected, 5,422 in the screening arm and 3,145 in the control arm. Polytomous regression showed that trial arm was associated with treatment choice after correction for missing values, especially in men with high-risk PC. A control subject with high-risk PC was more likely than a screen subject to receive radiotherapy (OR: 1.43, 95% CI: 1.01-2.05, p = 0.047), expectant management (OR: 2.92, 95% CI: 1.33-6.42, p = 0.007) or hormonal treatment (OR: 1.77, 95% CI: 1.07-2.94, p = 0.026) instead of radical prostatectomy. However, trial arm had only a minor role in treatment choice compared to other variables. In conclusion, a small effect of trial arm on treatment choice was seen, particularly in men with high-risk PC. Therefore, differences in treatment between arms are unlikely to play a major role in the interpretation of the results of the ERSPC.