Background: In Belgium, bladder cancer is the fifth most common cancer in males (5.2%) and the sixth mostfrequent cause of death from cancer in males (3.8%). Previous epidemiological studies have consistently reportedthat selenium concentrations were inversely associated with the risk of bladder cancer. This suggests that seleniummay also be suitable for chemoprevention of recurrence.Method: The SELEBLAT study opened in September 2009 and is still recruiting all patients with non-invasivetransitional cell carcinoma of the bladder on TURB operation in 15 Belgian hospitals. Recruitment progress can bemonitored live at http://www.seleblat.org. Patients are randomly assigned to selenium yeast (200 ìg/day)supplementation for 3 years or matching placebo, in addition to standard care. The objective is to determine theeffect of selenium on the recurrence of bladder cancer. Randomization is stratified by treatment centre. Acomputerized algorithm randomly assigns the patients to a treatment arm. All study personnel and participants areblinded to treatment assignment for the duration of the study.Design: The SELEnium and BLAdder cancer Trial (SELEBLAT) is a phase III randomized, placebo-controlled,academic, double-blind superior trial.Discussion: This is the first report on a selenium randomized trial in bladder cancer patients.