Abstract Background The Bladder Cancer Index (BCI) and Functional Assessment of Cancer Therapy-Bladder-Cystectomy (FACT-Bl-Cys) were developed to measure disease-specific health-related quality of life (HRQOL) in bladder cancer patients and patients treated with radical cystectomy, respectively. Both patient-reported outcome measures (PROMs) are frequently used in clinical practice, but are not yet validated according to the COSMIN criteria and not yet available in Dutch. Therefore, the aim of this study was to translate the BCI and FACT-Bl-Cys into Dutch and to evaluate their measurement properties according to the COSMIN criteria. Methods The BCI and FACT-Bl-Cys were translated into Dutch using a forward-backward method, and subsequently administered at baseline (pre-operatively) and 3 months post-operatively in bladder cancer patients who received a radical cystectomy. Validity (content and construct), reliability (internal consistency, test-retest reliability, and measurement error), floor and ceiling ...