Histologic criteria of low-grade vulvar/vaginal intraepithelial neoplasia (VIN1/VAIN1) are well established; however, a significant interobserver variability in diagnosing VIN1/VAIN1 has been reported. The goal of this study was to evaluate the utility of MIB-1 immunostaining as an adjunct test to increase the diagnostic accuracy in equivocal cases of VIN1/VAIN1. The second goal was to examine the distribution of low- and high-oncogenic risk human papillomaviruses (HPVs) in VIN1/VAIN1 lesions. Consecutive vulvar/vaginal biopsies originally diagnosed as VIN1/VAIN1 (n = 43) or benign (n = 20) were reviewed by two pathologists to obtain a consensus diagnosis. The diagnosis was further confirmed with HPV testing using Short PCR Fragment 10 and Line Probe Assay. MIB-1 immunostaining was performed, and positive staining was defined as a cluster of two or more stained nuclei in the upper two thirds of the epithelial thickness. After verification of the diagnosis using the consensus histologic review and HPV detection as an objective confirmatory test, 31% of cases originally diagnosed as VIN1/VAIN1 were identified as being overdiagnosed. The sensitivity and the specificity of MIB-1 staining for identifying VIN1/VAIN1 were 0.96 and 0.90, respectively. Seventy percent of VIN1 cases were associated with low-risk viral types. In contrast, the majority (84%) of VAIN1 cases were associated with high-risk HPVs. In conclusion, MIB-1 staining is sensitive and specific for identifying VIN1/VAIN1, helpful in verifying the diagnosis in equivocal cases.