PURPOSE: To compare inter- and intra-fraction bladder volume variations and bladder wall motion during radiotherapy (RT) for bladder cancer with full and empty bladder protocols. MATERIALS AND METHODS: Bladder volumes, filling rates and bladder wall movement were retrospectively analyzed for 24 patients with at least 4 sets of delineable pre and post treatment cone beam CT (CBCT)-scans. Eight patients were treated with an 'empty bladder' (EB) protocol and sixteen patients with a 'full bladder' (FB) protocol. RESULTS: 24 planning CT-scans and 356 CBCT-scans (178 sets) were analyzed. The average time between pre and post irradiation CBCT was 8min (range 6-18min). Median filling rate was 1.94ml/min and did not differ between EB and FB. Random variation in bladder volume and inter-fraction wall movement was slightly but not significantly larger for FB, whereas intra-fraction bladder wall movement was slightly but not significantly smaller for FB. The largest inter- and intra-fraction bladder wall movement was found in the cranial anterior direction. CONCLUSION: Empty and full bladder protocols show similar inter- and intra-fraction wall motion, and therefore treatment choices could be purely based on organ at risk criteria.