High Gleason score 8 to 10 adenocarcinoma is the most aggressive and potentially lethal form of prostate cancer. The 2005 International Society of Urological Pathology (ISUP)-modified Gleason grading scheme defines several gland arrangements of high Gleason grade patterns 4 and 5. The aim of this investigation was to quantitate the frequency of the ISUP-defined high Gleason grade patterns in needle biopsy tissue, to determine the common admixtures and to characterize patterns not presented in the 2005 ISUP report. For patients who underwent radical prostatectomy, we analyzed for association of specific high-grade patterns in needle biopsy with extraprostatic extension in radical prostatectomy tissues. A total of 268 prostate needle biopsy cases with Gleason score of 8 to 10 were examined. A mean of 3.6 patterns (range, 1 to 8) were identified per case and only 12% of cases had a pure single pattern. Ill-defined glands with poorly formed lumina (at 57%) and fused microacinar glands (at 53%) comprised the predominant and most frequently admixed patterns. Single cells and single signet ring cells were present in 53% and 31% of cases, respectively. Additional patterns in order of frequency included cords (35%), cribriform glands (25%), sheets of cells (19%), chains (4%), glomeruloid (3%), comedonecrosis (2%), and hypernephromatoid (1 case=0.3%). Gleason score 8 to 10 carcinomas are typically extensive in needle core tissue, with a mean of 4.4 positive cores (range, 1 to 15 cores) per case. Only 14 cases (5%) had high-grade minimal carcinoma measuring <1 mm in needle core tissue. Gleason grade patterns not described in the 2005 ISUP report include single file growth, solid cylinders, and nested patterns. The single file pattern was present in 40% of cases, and the small solid nested pattern was detected in 24% of cases. One case displayed solid cylinders. Only the single file pattern was associated with extraprostatic extension at radical prostatectomy (P=0.005). These results show that the 2005 ISUP-defined patterns of high Gleason score 8 to 10 prostatic adenocarcinoma can be stratified on the basis of frequency of occurrence in needle biopsy tissue. Three patterns not defined in the 2005 ISUP scheme have been characterized, including single file, nested, and solid cylinder arrangements. As aggressive and potentially lethal prostate cancer is most often of Gleason score 8 to 10, it is important for diagnostic recognition purposes to be aware of the frequency of various patterns encountered in high Gleason score 8 to 10 adenocarcinomas, the types of pattern admixtures, and the histomorphologic presentation of unusual patterns. We propose that Gleason grade assignments should incorporate single file, solid nested, and solid cylinder arrangements as high-grade pattern 5 because of the absence of glandular luminal space formation.