A 55-year-old woman had urinary frequency and a constant urge to urinate. Computed tomography confirmed a urethral tumor, and transurethral biopsy confirmed adenocarcinoma. She visited our hospital to undergo treatment, and we performed an anterior pelvic excenteration. On histology, the tumor had spread to the bladder, urethra, and vagina. However, the majority of the tumor was located in the bladder and urethra, a duct with intestinal metaplasia was present around the urethra, and carcinoma in situ was seen in the urethral mucosa. Based on the above findings, the patient was diagnosed as having primary urethral adenocarcinoma. No tumor cells were seen in the resection stump. Six months after surgery, the patient developed bone metastasis, followed by peritoneal and pleural dissemination, as well as multiple lung metastases. The patient died nine months after surgery. In the present patient, the carbohydrate antigen (CA) 19-9 level changed with the clinical course, and it was a useful marker. Urethral tumor is relatively rare. A urethral tumor accompanied by vaginal wall infiltration is likely to be mistaken for a primary vaginal tumor. It was very difficult to identify the primary organ in our case. To the best of our knowledge, the present patient is the sixth reported case of primary urethral carcinoma accompanied by vaginal wall infiltration in Japan. The six reported cases are compared and analyzed.