OBJECTIVE: This study aimed to evaluate outcomes and complications in dogs with urothelial carcinoma (UC) of the bladder trigone treated with total cystectomy using uretero-prepuce/vagina/cutaneous anastomosis combined with medical treatment. ANIMALS: Twenty-one dogs. PROCEDURE: Total cystectomy was completed as follows: The whole bladder and urethra were removed, and the ureters were anastomosed to the skin in 1 case and to the vagina in 9 cases in females. The entire bladder, prostate, urethra, and penis were removed, and the ureters were anastomosed to the prepuce in 11 males. Medical treatments were administered to all dogs after surgery. RESULTS: Short-term surgical complications included diarrhea (16 dogs), acute kidney injury (2 dogs), and dehiscence of the ureterovaginal anastomosis (3 dogs). Long-term surgical and medical complications included pyelonephritis (11 dogs) and chronic kidney disease (5 dogs). In the survival analysis, median survival time from the initial diagnosis in all cases was 481 d, which was longer than the previously reported median survival time in dogs with UC involving the trigone. CONCLUSION AND CLINICAL RELEVANCE: Total cystectomy combined with medical treatment prolonged overall survival compared with medical, surgical, or stenting procedures in dogs with UC involving the trigone.