Here we report the case of a urinary bladder leiomyoma in a rhesus macaque. The animal was clinically normal and had a lipoma localized to the stifle. Endovesicular leiomyomas are the most common form of urinary bladder leiomyoma in humans. In contrast, this macaque's tumor exhibited extravesicular localization in the bladder. Urinary bladder leiomyomas account for less than 0.5% of all bladder tumors in humans, with only 250 cases reported in total.