PURPOSE: The aims of this investigation were to access the relative ratio of epithelial types within the anal canal after a double-stapled ileoanal reservoir (DSIAR) and to review physiologic and functional differences based on this diversity in epithelial types. METHODS: According to types of the epithelium present at histologic sections of the distally excised tissue ring ("donut") after the stapling for restorative proctocolectomy with construction of a DSIAR, one hundred thirty-eight patients with ulcerative colitis were stratified into two groups: 40 patients (22 males and 18 females) were categorized to be of lower anastomosis (group I), where squamous, squamous mixed with columnar, or squamocuboidal component was reported to be present, and 98 patients (50 males and 48 females) to be of higher one (group II), which was evidenced by columnar epithelium at the "donut". Physiologic and functional parameters were appraised between 2 groups to define whether this difference in epithelial types is associated with a significant difference in postoperative anorectal functional outcome. RESULTS: None of preoperative parameters reflecting resting and squeeze pressures showed significant differences between 2 groups. Postoperative mean and maximal resting pressures (MRP and MxRP) were declined to 48.8 16.9 mmHg and 67.1 21.3 mmHg in group I, and 61.1 22.7 mmHg and 90.0 38.6 mmHg in group II, differences of which were significant (P=0.046 and 0.031, respectively). Neither postoperative mean nor maximal squeeze pressure was, however, statistically different between 2 groups. Mean length of the high pressure zone was decreased in both groups postoperatively, but there were no intergroup differences. Rectoanal inhibitory reflex decreased significantly from 97.4% to 50% in group I and from 86.5% to 53.9% in group II, respectively (P<0.0001 in both). However, there was no significant intergroup difference postoperatively. Maximal tolerance volume and compliance of the reservoir were significantly improved postoperatively in both groups; from 52.2 26.1 ml and 2.8 3.3 to 163.3 115.7 ml and 14.7 15.3 in group I (P=0.0001, and <.0001, respectively), and from 77.0 59.5 ml and 4.4 6.8 to 167.3 87.9 ml and 28.7 44.0 in group II (P<0.0001, both). But there was no intergroup difference in either parameters postoperatively. There were no significant differences between groups relative to functional outcome except the diurnal incontinence to solid stool (P<0.011). CONCLUSIONS: Although epithelial types were shown to be variable at the anal side of the anastomosis after a DSIAR, these differences were not associated with physiologic and functional differences. Therefore, if technically feasible, this procedure can be performed with safety without fear of significant functional derangement.