Vulvar intraepithelial neoplasia (VIN) is the currently accepted generic de
signation for the spectrum of vulvar lesions with the histologic features o
f squamous dysplasia and squamous cell carcinoma in situ. Although several
classifications of VIN have been espoused in the past 20 years, VIN can be
readily classified into two principal clinicopathologic types: classic (bow
enoid) VIN and simplex (differentiated) VIN. This manuscript summarizes the
historical development and current status of our knowledge about VIN. Info
rmation on the clinical and pathologic aspects are detailed and illustrated
, as are considerations of differential diagnosis.