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Prior studies have not analyzed grading patterns and accuracy in nonacademic sites and have not analyzed reasons for discrepant grades. We analyzed 499 radical prostatectomy (RP) specimens at The Johns Hopkins Hospital (JHH) from 1994 and compared them with the corresponding JHH needle biopsy Gleason grade and, when available (n = 390), to the outside institution (non-JHH) Gleason biopsy grade. For JHH, there was exact agreement between biopsy and RP in 58% and agreement to within one digit in 93% of cases, compared with 34% and 67%, respectively, for non-JHH. Combining cases into more meaningful groups (Gleason 2-4, 5-6, 7, and 8-10), there was 66% exact correlation between the biopsy and RP for JHH as compared with 45% for non-JHH. Non-JHH undergraded biopsy results more than JHH, with 22.3% and 1.2% Gleason score 2-4, respectively. None of the cases with a Gleason score of 2-4 on biopsy from JHH or non-JHH were Gleason score 2-4 on RP. Fifty-five percent of the tumors with non-JHH needle biopsy results graded Gleason 2-4 had either capsular penetration, seminal vesicle, or lymph node involvement. All of the tumors with needle Gleason score 2-4 at JHH were organ confined. The JHH needle biopsy grade correlated better with pathologic stage than did non-JHH (R = 0.27 JHH vs. R = 0.12 non-JHH). Extent of cancer in the biopsy sample was not a factor in the accuracy of predicting RP grade or stage. Eighty-two cases evaluated at JHH were signed out by a genitourinary pathologist; the grading of the biopsy samples by other JHH pathologists was just as accurate. Gleason score of ≥7 on the biopsy sample predicted a Gleason score of ≥7 in the RP 87.5% of the time. A Gleason score of <7 predicted a Gleason score of <7 only 63.9% of the time. Discordant grades in some cases reflected patterns of cancer on needle biopsy that were borderline between two different Gleason scores. Sampling was the major source of discrepancy and was often due to the high-grade component in the RP not being present in the biopsy results or due to a component of cancer on the needle reflecting such a small percentage of the pattern seen on RP that this pattern was not included in the final RP Gleason score.