The ultimate goal of prognostic assessment is optimization of individual counseling. Often, however, studies on prognostic factors focus on discriminating between high risk and low risk subgroups without considering the relevance of 1 or more factors for predicting disease outcome in individual patients. We quantified the accuracy of prediction of future recurrences and disease progression in individual patients with primary superficial bladder cancer. The study cohort consisted of 1,674 patients who were followed prospectively between 1983 and 1991 in the Netherlands. By analyzing half of the patients with proportional hazards regression, we computed relative risks of recurrence and progression. A prognostic index score based on these relative risks was then applied to the other half of the patients to determine whether group outcome could be predicted accurately. To assess the accuracy of prediction in individuals we used a method similar to the construction of receiver operating characteristic curves in diagnostic test assessment. The 3-year risk of first recurrence was 55% (95% confidence interval 51 to 59%). The 3-year risk of first progressive disease was 10% (95% confidence interval 8 to 12%). For the risk of first recurrence, tumor stage, tumor extent and multicentricity had statistically significant prognostic ability. Prognostic factors for the risk of disease progression were tumor stage, grade, multicentricity and the result of random biopsies from cystoscopically normal-appearing urothelium. For patients with a prognostic index score that suggested a low risk for recurrent and progressive disease the predicted 3-year risk of first recurrence was still 44% but the predicted 3-year risk of progression was only 3%. For patients with a prognostic index score that suggested a high risk the predicted risks were 74% and 22%, respectively. These predicted risks appeared to be fairly accurate when applied to the other half of our case series. However, in any 2 patients chosen at random the chance that the patient with the worst predicted prognosis would have a shorter recurrence-free and progression-free followup was calculated to be only 58% and 67%, respectively. Although the available prognostic factors in superficial bladder cancer may be useful to identify high risk and low risk subgroups, predictability in individuals is highly inaccurate. More relevant prognostic factors are needed to decrease current overtreatment and undertreatment rates, and to improve the followup policy.