Occult bladder injury may sometimes go unrecognized during tension-free vaginal tape (TVT) procedures. We report a case of occult intraperitoneal bladder injury that occurred during a TVT procedure. There was no sign of bladder perforation on the initial cystoscopy, which was performed just after the insertion of the trocar. Signs of general peritonitis appeared after the patient started to void the next day. A postoperative cystogram and cystoscopy showed an intraperitoneal bladder injury and a pinhead-sized ulcerative lesion in the right lateral wall of the bladder. We suspect that at the time of initial cystoscopy, the trocar passed through the submucosal area without violating the bladder mucosa. The occult bladder injury may have been caused after the initial cystoscopy by advancing the rough edge of the prolene tape during the extraction of the trocar. This report is the first description of such an occult bladder injury during a TVT procedure.