I read with great interest the article by Cooperberg and coworkers 1 studying survival rates in differently treated men with early prostate cancer. In this study, patients who underwent radical prostatectomy had a substantially decreased disease-specific mortality, particularly in the higher-risk groups, compared with those who were selected for radiation therapy or conservative management. 1 Unlike Cooperberg et al., I do not consider it unlikely that unmeasured confounding, at least in part, accounted for the observed differences. It is conceivable that patients with a particularly adverse profile within the same risk category might have preferably been referred to external-beam radiotherapy, thus putting this treatment modality at a disadvantage. It is questionable whether this phenomenon is adequately covered by conventional prognostic factors because subjective clinical judgment is included. Selection in favor of surgery is a problem when different treatments for early prostate cancer are compared. 2,3 Even careful risk adjustment will hardly be able to eliminate this effect completely. 3,4 Otherwise, it would be difficult to justify randomized trials comparing radical prostatectomy and external-beam radiotherapy in this setting that the authors rightly called for. 1