The distinction of basal cell hyperplasia (BCH) from carcinoma or high-grade prostatic intraepithelial neoplasia may be difficult. We reviewed 25 cases of BCH with unusual features and identified four distinct groups: BCH with intracytoplasmic globules (five cases); BCH with calcifications (eight cases), including one with globules; BCH with squamous features (three cases); and cribriform BCH (nine cases), including two cases with globules. A total of five cases contained prominent nucleoli and/or cytologic atypia. Hyaline cytoplasmic globules have not been described in any other prostatic entity and appear diagnostic of BCH. Calcifications observed in BCH were psammomatous, differing from the fine stippled calcifications occasionally seen in areas of comedonecrosis within high-grade prostatic carcinoma. Basal cell hyperplasia with squamous features differed from squamous differentiation in carcinomas (adenosquamous carcinoma) and from benign foci of squamous differentiation seen associated with either prostatic infarcts or with hormonal therapy. Whereas cribriform prostatic intraepithelial neoplasia and cribriform cancer glands represent a single glandular unit with punched out lumina, many of the glands within a focus of cribriform BCH appeared as fused individual BCH glands. The use of cytokeratin 34betaE12 can help in difficult cases. In cribriform BCH high-molecular-weight cytokeratin shows multilayered staining of the basal cells in some of the glands and a continuous layer of immunoreactivity. Cribriform prostatic intraepithelial neoplasia demonstrates an interrupted immunoreactive single cell layer of basal cells. Recognition of the architectural and cytologic features of unusual morphologies of BCH can be used to facilitate its diagnosis and differentiation from prostatic carcinoma and high-grade prostatic intraepithelial neoplasia.