Damage to the bladder during inguinal hernia repair is possible especially if the bladder or a bladder diverticulum is involved in the hernia sac. Unrecognized injury to the bladder can lead to late complications. We report a case of pseudotumor in a bladder diverticulum due to long-term retention of a misplaced suture. The literature on bladder injury after inguinal herniorrhaphy and on pseudotumor formation is briefly reviewed. It is important to be aware of a history of inguinal surgery and to obtain definitive histologic evidence of malignancy prior to making the diagnosis of bladder carcinoma. This will avoid unnecessary radical surgery, chemotherapy, or radiation therapy.