Urachal cystadenocarcinoma (UC) is a rare but highly aggressive subtype of bladder cancer. While most localized cases of UC are asymptomatic, occasionally, patients present with nonspecific lower urinary tract symptoms. Unfortunately, most cases are not detected until advanced disease is present. The presence of local nodal or distant metastasis is particularly important for prognosis, drastically reducing five-year overall survival rates. The gold standard for localized UC is wide surgical excision, with no established role of chemotherapy. On the contrary, endometrial carcinoma (EC) is the most common gynecologic malignancy. As such, staging, prognosis, and treatment guidelines of endometrial carcinoma are well-established. The gold standard treatment for localized endometrial carcinoma includes total abdominal hysterectomy and bilateral salpingo-oophorectomy (TAH-BSO) and lymph node dissection (LND). Concurrent cases of urachal cystadenocarcinoma and endometrial carcinoma are exceedingly rare. To the authors' knowledge, there have been no known reports of these co-occurring malignancies thus far in the literature. We present the case of a 66-year-old patient with nonspecific lower urinary symptoms and incidentally discovered UC in the setting of concurrent endometrial carcinoma. The patient underwent robotic excision of the urachal cystadenocarcinoma and TAH-BSO, followed by adjuvant chemotherapy and vaginal brachytherapy. Surveillance imaging at 16 weeks after surgery showed no evidence of disease recurrence.