Urinary diversion through intestinal segments is a widely used method after radical cystectomy. During the last few years, new methods of bladder substitution, continent ileal neobladders, were developed. We used the method described by Hautmann et al. in 1986. 70 cm of ileum is used to form a reservoir. The ureters are implanted into the reservoir, which is then anastomosed to the urethral stump. A known problem when intestine is used for urinary diversion is the absorption of urinary solutes leading to metabolic disturbances. Therefore, the absorption of vitamin B12, instilled into the neobladders of 20 patients, was measured and related to the postoperative interval. The results show a high absorption rate 2 weeks postoperatively that is reduced quickly and significantly (p < 0.001) within the first 10 months (from more than 30 to below 5%). One year to 23 months after the operation, some neobladders absorbed no vitamin B12 at all, whereas others still absorbed significantly but only small quantities. These results may probably be attributed to the loss of villous structure as well as atrophy of the epithelial surface.