The clinicopathologic features of five cases of verrucous carcinoma of the vulva and their staining pattern with antikeratin monoclonal antibodies AE1 and AE3 were compared with those of conventional squamous cell carcinoma. Two patients had local recurrences but none died of the tumor. AE1 and AE3 antibodies stained the entire epithelial thickness in both verrucous and squamous cell carcinoma, but in the former the positivity was uniform and homogeneous everywhere, while in squamous cell carcinoma the positivity was extremely disorganized and patchy. The pattern of expression of monoclonal antibodies AE1 and AE3 confirms that verrucous carcinoma is an extremely well-differentiated squamous neoplasm in contrast to squamous cell carcinoma, which is heterogeneous from a viewpoint of differentiation.