Biopsy and surgical specimens were studied from two patients with squamous cell carcinoma in situ of the vulva and one with verrucous carcinoma of the vulva. All three patients subsequently developed invasive squamous cell carcinoma of the vulva. In two, human papillomaviruses (HPVs) 16 and 18 were found in the lesions before the development of invasive carcinoma. In the specimens with invasive squamous cell carcinoma, HPV 16 or 18 or both was found. The third patient had HPV 18 DNA in the specimen demonstrating squamous cell carcinoma in situ; when invasive squamous cell carcinoma was diagnosed 9 years later, HPVs 16 and 18 were found in the latter lesion. These findings lend support to the role of HPVs 16 and 18 in the development of invasive squamous cell carcinoma of the vulva.