The objective of the study is to evaluate the post-operative effect of an orthotopic ileal neobladder or a Mainz pouch I bladder replacement on the extent of intestinal oxalate absorption. Gastrointestinal oxalate absorption was measured in six patients with an orthotopic ileal neobladder and in six patients with a Mainz pouch I bladder replacement. The function test applied was the [13C2]oxalate absorption test. With a range of 5.1-12.4%, the oxalate absorption of these patients was well within the reference range for healthy volunteers. The results from our small study indicate that such continent urinary diversions present no hazard for oxalate hyperabsorption and subsequent calcium oxalate urolithiasis.