Aim. To improve the instant results of urinary bladder reconstruction with iliac graft by examination of critical zones. Methods. Urinary bladder reconstruction using the iliac autograft was performed in 15 patients without special examination of critical zones (control group) and in 25 patients in whom these zones were examined (main group). Mean age of patients was 58 years (from 44 to 68). All patients underwent cystectomy because of urinary bladder cancer (stages T2-4N0M0). Blood microcirculation at the stitch area was performed by M.Z. Sigal, tissue viability index by M.R. Ramazanov was calculated, oxygen saturation of arterial blood was measured and microcirculatory blood flow was examined by the LAKK-01 machine. The same surgery and research methods were performed in 70 dogs with regular assessment of microcirculation at the stitch area (stitch color, arterial pulsation) and using the tensiometry by M.Z. Sigal, microcirculation at the stitch area, oxygen saturation of arterial blood and stitch tissue viability index were also determined. Results. In patients of the control group, in whom the condition of critical zones was not examined, 3 has developed a stitch dehiscence at the zones of anastomosis, with no such events registered in patients from the main group, in whom critical zones were examined. In dogs stitch dehiscence was not observed only in the group where microcirculation was assessed by tissue viability index calculation. Conclusion. It is important to examine critical zones of the iliac autograft and calculate the stitch tissue viability index performing urinary bladder reconstruction with iliac graft to prevent the stitch dehiscence.