Pseudocarcinomatous hyperplasia is not fundamentally a hyperplasia of epidermal epithelium, but rather a hyperplasia of adnexal epithelia, namely, of follicular infundibula and eccrine ducts. All examples of pseudocarcinomatous hyperplasia are responses to an underlying inflammatory or neoplastic process. That process can usually be discerned beneath the pseudocarcinomatous hyperplasia in the biopsy specimen. Application of criteria that pertain mostly to architectural pattern (silhouette) enables pseudocarcinomatous hyperplasia to be differentiated histopathologically from squamous cell carcinoma.