Pagetoid urothelial carcinoma in situ (CIS) is a rare variant of bladder cancer that is characterized by an intraepithelial proliferation of large cells arranged singly or in clusters and randomly distributed. These neoplasms deserve recognition and attention, chiefly because they may be overlooked or misdiagnosed as urothelial dysplasia, then causing unsuspected tumor recurrence after surgery. We report on the clinicopathological features and immunohistochemical findings of 11 (14.86%) cases of pagetoid CIS in a retrospective study of 74 cases of conventional carcinoma in situ. Most patients were male ( n=10). Their ages ranged from 31 years to 78 years. The lesion can be present with primary ( n=2) or secondary ( n=9) CIS. Pagetoid CIS is usually a focal lesion occurring in a clinical and histological setting of conventional CIS, and these patients essentially have the same progression and survival rates as patients without pagetoid changes and are treated in the same way. In cases with extensive urothelial denudation, pagetoid CIS may be focally present in otherwise normal-looking urothelium, thus alerting the pathologist to search for additional CIS elsewhere in the bladder. Given that primary extramammary Paget disease of the external genitalia and of the anal canal may extend to the bladder and, conversely, some bladder cases of pagetoid CIS may extend to the urethra, ureter, and beyond to the external genitalia, the differential diagnoses between these two entities represent an important therapeutic consideration. Our data suggest that a panel of immunostains including CK7+/CK20+/TM+ may assist in differentiating urothelial pagetoid CIS from extramammary Paget disease which is known to be CK7+/CK20-.