Vulvar intraepithelial neoplasia (VIN) is a premalignant condition of the vulva. VIN is synonymous with high-grade squamous intraepithelial lesion (HSIL) of the vulva. What was previously known as VIN 1 is now referred to as low-grade squamous intraepithelial lesion (LSIL) of the vulva. Current terminology equates "VIN" with HSIL, because LSIL of the vulva does not represent a true premalignant condition, but rather is a sign of human papillomavirus (HPV) infection. (See genital wart.)

The most common form is usual type VIN, which is associated with infection by HPV. The other (and less common) form is differentiated VIN, which is associated with dermatologic conditions of the vulva, especially lichen sclerosus. Differentiated VIN is more likely to be associated with vulvar squamous cell carcinoma and is more likely to recur.

Usual type VIN is becoming more common, especially among women in the fifth decade of life. Risk factors for usual type VIN include HPV infection, tobacco use, and immunocompromised state (same risk factors as high-grade cervical dysplasia). Differentiated VIN is more common in postmenopausal women with vulvar dermatoses, especially if left untreated.

Patients with VIN may present with a vulvar lesion detected by themselves or a partner. In patients who present with a complaint, vulvar pruritus is the most common. Less commonly seen are complaints of pain (eg, with urination or intercourse) or burning. Nearly half of patients diagnosed with VIN are asymptomatic. In these cases, the lesion is first identified during a physical exam.