The incidence of concomitant prostate adenocarcinoma found in patients with muscle-invasive bladder carcinoma is not uncommon, reaching up to 21%–28%. However, the presence of collision metastasis involving prostate cancer and bladder cancer within the same lymph node is exceedingly rare, with only 5 cases reported to date in the literature. We report a case of collision metastasis of prostate adenocarcinoma and urothelial carcinoma of the bladder in a 73-year-old man who underwent cystoprostatectomy with bilateral pelvic lymph node dissection for high-grade muscle-invasive urothelial carcinoma. Final pathology revealed a pT3aN2 high-grade urothelial carcinoma and pT3N1 Gleason 4 + 4 = 8 adenocarcinoma of the prostate with 12/40 pelvic lymph nodes positive for urothelial carcinoma. One node was positive for both urothelial carcinoma and prostate adenocarcinoma, confirmed by positive staining by p40 and prostate specific antigen(PSA), respectively. Immunohistochemistry is the sole method of confirming collision metastasis of two primary cancers. In this case, we describe immunohistochemical markers for urothelial carcinoma and prostate adenocarcinoma and their clinical implications. One month postoperatively, our patient began adjuvant leuprolide therapy and cycle 1 of gemcitabine and cisplatin chemotherapy, which he is tolerating well.