Our interest in verruca plana and epithelial nevus was prompted by the observation that the vacuolar alterations of epidermal cells in both of these conditions suggested a possibly common pathologic anomaly. We were impressed particularly by the morphologic relations of verruca plana and epidermodysplasia verruciformis, and, in fact, this investigation was undertaken when we had the opportunity recently to examine patients suffering from epidermodysplasia verruciformis at the Mayo Clinic and sought to distinguish histologically between this disease and verruca plana, which it grossly simulates. Also, one of us (H. M.)1 has recognized for many years the fact that apparently related epidermal abnormalities occur in some forms of linear nevus. It was the purpose of this study to determine whether the epidermal lesion in verruca plana is the same as the lesion in certain forms of epithelial nevus and also to appraise the nosologic status of epidermodysplasia verruciformis, which has