To investigate the recently described Lee mortality index as predictor of mortality after radical cystectomy. A total of 735 patients who underwent radical cystectomy for bladder cancer between 1993 and 2010 were studied. Median patient age was 67 years and the median follow-up was 7.8 years (censored patients). The Lee mortality index was assigned based on data derived from patient history, preoperative cardiopulmonary risk assessment and discharge records. The age-adjusted Charlson score and preoperative cardiopulmonary risk assessment classifications were used for comparison. Competing risk analysis and Cox proportional hazard models for competing risks were used for the statistical analysis. The Lee mortality index predicted competing mortality in a dose–response relationship with somewhat lower 10-year mortality rates than predicted (p = 0.0120). Beside the age-adjusted Charlson score, the Lee mortality index was an independent predictor of overall mortality (hazard ratio per unit increase 1.06, p = 0.0415) and replaced the age-adjusted Charlson score as predictor of competing mortality (hazard ratio (HR) per unit increase 1.27, p < 0.0001). The American Society of Anesthesiologists (ASA) physical status classification was also an independent predictor of overall (HR for ASA 3–4 versus 1–2: 1.53, p = 0.0002) and competing mortality (HR for ASA 3–4 versus 1–2: 1.62, p = 0.0044). The Lee mortality index is a promising and easily applicable tool to predict competing mortality after radical cystectomy. It is at least equal to the age-adjusted Charlson score and may be supplemented by information provided by the ASA classification.