Bladder diverticulum, which can be present in 1% to 10% of the general population, is an outpouching of the bladder urothelium through the muscular bladder wall. The vast majority of bladder diverticula are acquired and occur more commonly in men with neurogenic dysfunction or bladder outlet obstruction. Due to the lack of a muscular layer, bladder diverticulum loses its contractility and ability for effective urine emptying, which increases the risks of chronic inflammation and malignant transformation. Neoplasms arising within diverticula are uncommon, which vary from 0.8% to 13% of vesical diverticulum cases reported and have the potential to invade perivesical tissues. During routine educational dissection of a 75-year-old male cadaver with a history of bladder cancer, two bladder diverticula were found on the right superolateral aspect of the posterior and anterior walls. Grossly, the bladder wall was thickened and trabeculated with no masses identified, and the prostate was enlarged. Postmortem histopathological evaluation revealed a high-grade urothelial carcinoma of the bladder diverticulum and benign prostatic hyperplasia. There was no evidence of metastasis from tissue samples taken from the liver, lungs, inguinal lymph nodes, and kidneys. Bladder cancer arising within a diverticulum has a poor prognosis and is difficult to diagnose and treat due to its early transmural invasion, tendency for higher histopathological grades, and late clinical presentation. This case is an example of an unusual manifestation of diverticular diseases that is critical for clinicians to recognize. Appropriate screening and early treatment for patients with diverticula secondary to bladder outlet obstruction should be considered to prevent further complications.