With high-grade prostatic intraepithelial neoplasia with adjacent small atypical glands (PINATYP), the issue is whether the small glands represent budding or tangentially sectioned glands off of adjacent high-grade prostatic intraepithelial neoplasia (PIN) or invasive cancer next to high-grade PIN. The histology and significance of PINATYP on biopsy have not been described. Among 574 cases of high-grade PIN lesions on needle biopsy, we identified 71 cases of PINATYP. Most cases were consultations, and 51 cases were available for histologic review. At least 1 follow-up prostate biopsy was performed in each of 55 cases. Immunohistochemistry for high-molecular-weight cytokeratin (HMWCK) was performed on cases in which material was available. The average patient age at diagnosis was 65.5 years (range, 48 to 103 years). The initial digital rectal examination, transrectal ultrasound, serum prostate-specific antigen (PSA) level, PSA velocity, and family history of prostate cancer did not predict cancer on repeat biopsy. In 39% of cases, high-grade PIN had a predominantly flat pattern, and remaining cases showed a predominance of other patterns (tufting, micropapillary, cribriform). The average number of high-grade PIN glands and adjacent small atypical glands were 11.5 (1 to 60) and 5.3 (1 to 21), respectively. The farthest adjacent small atypical gland averaged 0.12 mm from the high-grade PIN (0.01 mm to 0.4 mm), as measured with an ocular micrometer. The following histologic features did not predict cancer on repeat biopsy: more than 1 core involved by the high-grade PIN; number of high-grade PIN glands; number of small atypical glands; distance of small atypical glands from the high-grade PIN; size and percentage of nucleoli; marked nuclear pleomorphism; and mitoses. Overall, the risk of cancer on repeat biopsy was 46%. Two findings predicted a lower risk of cancer on repeat biopsy: younger age (62.2 years benign v 68.3 years cancer; P =.004) and predominantly flat high-grade PIN (P =.007). In our material, PINATYP appears to be a greater risk factor than high-grade PIN alone in predicting cancer on rebiopsy. Although age and predominant pattern of associated high-grade PIN may be helpful in predicting which men with this lesion will have cancer on rebiopsy, they cannot be used reliably; therefore, all men with PINATYP should undergo repeat biopsy. HUM PATHOL 32:389-395.