The histologic findings of five patients with clinically typical Bowenoid dysplasia (BD) allowed the authors to classify the vulvar and perineal biopsies of 18 patients under 40 years as BD and the vulvar biopsies of six patients under 40 years as squamous cell carcinoma in situ (CIS). The two best criteria for BD are cellular uniformity and absence of pilosebaceous involvement. Vesicular chromatin is a less constant feature of BD. Clinically, patients with BD were younger than those with CIS, more frequently had elevated and multiple lesions and often developed BD with pregnancy. Histologic features therefore discriminate between clinical BD and CIS, but the authors emphasize that both clinical and pathologic features are necessary for proper diagnosis. Follow-up of BD has been benign, with one exception. Spontaneous regression occasionally occurred. One patient with CIS developed microinvasive carcinoma. Patients with BD were regarded at lesser risk for invasive carcinoma than patients with CIS; they are therefore amenable to conservative therapy.