SOX2 is a transcription factor controlling pluripotency in both embryonic stem cells and adult tissue-specific stem cells. SOX2 has been reported as an important factor in squamous cell carcinomas (SCC) of different locations and is involved in tumorigenesis. We evaluated the expression of SOX2 in vulvar non-neoplastic and neoplastic epithelia to test whether it is related to neoplastic progression. SOX2 immunoexpression was evaluated in 101 formalin-fixed, paraffin-embedded archival vulvar epithelia consisting of normal squamous vulvar epithelia (n=25), lichen sclerosus (n=9), high-grade classic vulvar intraepithelial neoplasia (HG-VIN, n=16), differentiated vulvar intraepithelial neoplasia (d-VIN, n=18), and vulvar invasive keratinizing SCC (n=33). Immunoexpression of SOX2 was nuclear and increased stepwise from normal vulvar epithelia/lichen sclerosus to HG-VIN and d-VIN (P<0.0001), from HG-VIN and d-VIN to invasive SCC (P=0.0029), and followed the morphologic distribution of atypical squamous epithelial cells. Scores for normal vulvar epithelia versus lichen sclerosus and HG-VIN versus d-VIN, respectively, did not differ significantly. SOX2 expression increased from tumor Grade 1 to 3 (P=0.0124); there was no relation to recurrence and survival. This is the first study presenting SOX2 as overexpressed in vulvar intraepithelial and invasive squamous lesions. This overexpression apparently reflects an early event in the neoplastic transformation of vulvar squamous epithelia. However, SOX2 seems to play a role in histologic dedifferentiation to Grade 3 invasive SCC too, and may be relevant to vulvar carcinogenesis.