It has been proposed that low-grade vulvar and vaginal lesions (VIN 1 and VaIN 1) are flat condylomas and should be designated as such. Moreover, their relationship to high-grade lesions (VIN 3 and VaIN 3) is unclear. Accordingly, this study was undertaken to address these issues by comparing the distribution of human papillomavirus (HPV) types in vulvar and vaginal intraepithelial lesions. We identified 33 cases of VIN 1, 34 cases of VIN 3, 17 cases of VaIN 1, and 16 cases of VaIN 3. In addition, 36 cases of low-grade squamous intraepithelial lesion (LSIL) in the cervix and 116 cases of cervical high-grade squamous intraepithelial lesion were used for comparison. Polymerase chain reaction analysis was performed using both the Roche PGMY and DDL SPF 10 systems. In cases where HPV was detected, the majority of low-grade and high-grade lesions contained a single HPV type. However, a minority of cases were found to have multiple HPV types. Of the VIN 1 cases, a low-risk virus was seen in 22 (67%), with HPV 6 or 11 accounting for 14 (42%). A high-risk virus was detected in 14 (42%) of cases of which 2 (6%) contained HPV 16. Of the VIN 3 cases, all had high-risk HPV of which 31 (91%) were found to have HPV 16. Of the VaIN 1 cases, 6 (35%) were found to have low-risk HPV types. HPV 6 or 11 were not found in these cases. High-risk virus was seen in 13 (76%) VaIN 1 cases, with 1 (6%) containing HPV 16. HPV was detected in 15 of 16 (94%) VaIN 3 lesions, all of which had high-risk types. HPV 16 was found in 8 (50%). In contrast, 2 (6%) of cervical LSIL had low-risk HPV (HPV 6 and 11), whereas 34 (94%) of LSIL cases had high-risk HPVs. Of the cervical high-grade squamous intraepithelial lesion cases, 100% had high-risk HPVs of which 87 (75%) were found to have HPV 16. The findings demonstrate that a significant number of low-grade vulvar and vaginal lesions contain high-risk HPV types, supporting their designation as low-grade intraepithelial lesions rather than flat condylomas. The low frequency of HPV 16 in VIN 1 compared with VIN 3 suggests they are distinct lesions or that HPV 16 is critical in the progression to VIN 3. Finally, comparison of the distribution of HPV in the vagina and vulva suggests that VaIN is more closely related to cervical intraepithelial neoplasia than to VIN.