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We present the first case of an unusual ureteral diverticular lesion demonstrating similarities to adenomyomatous hyperplasia of the gallbladder. A 68-year-old asymptomatic Japanese man with high prostate-specific antigen levels was clinically evaluated. Left hydronephrosis and benign prostatic hyperplasia were detected. A bilateral retrograde pyelogram revealed that the upper and middle portions of the left ureter exhibited an irregular narrow lumen and some pooling of contrast material, which was compatible with ureteral pseudodiverticulosis. Although no malignant cells were seen on cytology, computed tomography detected a fusiform shaped lesion with a circumferential thick wall including multiple diverticulae. Left nephroureterectomy was performed because malignancy could not be ruled out. Pathology demonstrated that the ureteral lesion showed a localized thick wall consisting of multilocules and/or multicysts and a hyperplastic muscularis propria. The cysts were mostly seen in the muscularis propria or a deeper site. The inner layers of the cysts were lined with normal urothelium, and some cysts opened onto the mucosal surface, indicating that they were derived from invaginated mucosal epithelium. We believe that this lesion may be a novel form of diverticular disorder demonstrating similarities to adenomyomatous hyperplasia of the gallbladder.