Abstract: The aim of this study was to characterize the aggressiveness of prostate cancer as assessed by the Gleason score (GS), the predominant Gleason pattern (pGP), and testosterone (T) serum concentration.: A total of 247 patients, referred to our Department (from January 2007 to December 2009) for a radical prostatectomy, underwent preoperative T and bioavailable testosterone (samplings between 07:00 and 10:00 h). Serum determinations (radioimmunoassayed in a central laboratory). GS and pGP were determined in prostate biopsies and prostate tissue specimens.: In biopsy specimens, a GS7 was observed in 105 (43%) patients; 25 (10%) had pGP4. In prostate specimens, 163 (66%) had a GS7; 60 (24%) had pGP4. For prostate specimens, comparing the 75 patients with pGP4 (GS 4+3, 4+4 and 4+5) to the 172 with pGP3 (GS 3+3 and 3+4), T was lower (4.03 vs. 4.75 ng/mL, p=0.003) and prostrate-specific antigen (PSA) higher (11.1 vs. 7.3 ng/mL, p<0.00001). Extra prostatic extension and positive margins were observed more frequently (52% vs. 18%, p<0.000001 and 29% vs. 15%, p=0.009, respectively). The 40 patients with T <3.0 ng/mL were larger (+5 kg, body mass index: +1.7 kg/m: Aggressiveness of the tumor cannot be properly estimated by the GS and pGP found in biopsies. The pGP in prostate specimens is of paramount importance, particularly in the case of a Gleason 7, to appreciate the outcomes and to choose the treatment. Preoperative testosterone should be added to PSA determination to improve prediction of treatment outcomes.