A 60-year-old man underwent radical prostatectomy for biopsy-proved adenocarcinoma of the prostate. Histologic examination of the entirely embedded prostatectomy specimen revealed extensive ordinary adenocarcinoma, Gleason's grade 3 + 3 = 6, involving both sides of the gland, and extending into extraprostatic soft tissue at the left base. Adjacent to the carcinoma, and separately, extensive high-grade prostatic intraepithelial neoplasia (PIN) was identified, much of which showed bland nuclei and abundant xanthomatous cytoplasm, identical morphologically to that seen in foamy gland prostate carcinoma. However, unlike foamy gland carcinoma, the foamy glands in the current patient were large, showed papillary infolding, and were associated with a discontinuous layer of basal cells, demonstrated by immunostaining for high-molecular weight cytokeratin. No invasive foamy gland carcinoma was identified in the prostatectomy specimen. Immunostains for Ki-67 showed an increased proliferation rate in foamy high-grade PIN glands when compared with adjacent benign glands. Review of additional outside biopsy material revealed foamy gland high-grade PIN on four of seven needle cores, two of which showed no carcinoma. This patient demonstrates a new subtype of high-grade PIN that is difficult to recognize on needle biopsy. It is important to distinguish foamy gland high-grade PIN from its infiltrating counterpart, and it is critical to recognize because of the association of high-grade PIN with prostate carcinoma.