Introduction The aim of this article was to evaluate the effectiveness of the Gleason grade groups (GGG) system on a group of Argentinian patients with prostate cancer (PC) who underwent radical prostatectomy (RP). Material and methods We retrospectively studied 262 patients who underwent RP between 1996 and 2014. To determine the performance and validity of the GGG system, a Kaplan-Meier analysis and multivariate analysis with Cox proportional method were performed to evaluate biochemical recurrence, distance metastases and specific cancer mortality. The area under the curve (AUC) was calculated to compare new groups of degrees of the GGG system with the classical scheme of stratification into 3 groups. Results The median follow-up was 84 months. As the groups ascend, there is less confined organ disease (p <0.001) and greater extraprostatic extension (p <0.001), greater invasion of seminal vesicles (p <0.001) and greater lymph node involvement (p <0.001). The biochemical recurrence-free survival at 5 years was 68%, 55%, 22%, 9%, 0% of the 1–5 groups, respectively. Ten-years cancer-specific survival was 96%, 95%, 78%, 64%, 25% for group 1–5, respectively. In the multivariate analysis, the GGG system is presented as the only independent predictor of biochemical recurrence and specific cancer mortality. The AUC indicates that the GGG system has a higher prognostic discrimination compared to the classic 3-group system (6, 7, ≥8). Conclusions The International Society of Urological Pathology (ISUP) GGG system is an independent predictor of biochemical recurrence and mortality from prostate cancer in patients treated with RP. The classification into 5 groups shows greater discrimination in the prognosis than the traditional Gleason classification.