['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\xa0h). 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\xa0ng/mL, p=0.003) and prostrate-specific antigen (PSA) higher (11.1 vs. 7.3\xa0ng/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\xa0ng/mL were larger (+5\xa0kg, body mass index: +1.7\xa0kg/m2), PSA was higher (9.9 vs. 8.2\xa0ng/mL, p=0.07). They had a higher percent of GS with pGP4: 53% vs. 25% (p=0.0008).'] Are preoperative low serum testosterone levels associated with tumor aggressiveness in radical prostatectomy treated cancer patients?