Objective: Our aim was to evaluate the effects of glucose levels and diabetes mellitus in prostate cancer (PCa) biology. Materials and methods: Two PCa cell lines (LNCap and PC3) were cultured in RPMI medium with different glucose concentrations [5mM (LG) and 25mM (HG)]. Expressions of androgen receptor, Her2/neu and glucose transporters (GLUT1, 3, 5 and 12) were evaluated by flow cytometry. Proliferation rate was assessed by colorimetric assay MTT and cellular characterization was performed by haematoxylin and eosin staining. Additionally, we performed a cross sectional analysis of 704 patients undergoing radical prostatectomy who were divided into two groups (diabetic and non-diabetic). An analysis of clinical and histological data seeking to identify the differences on tumor aggressiveness between the two groups was performed. Results: In LNCaP cell line, when the glucose concentration in the medium increased, there was an increased in AR expression. Regarding expression of Her2/neu receptor, medium’s glucose concentration significantly changed the expression of this receptor in both PC3 and LNCaP cell lines. Growth rate was higher on the HG medium for both cell lines. The clinical study of patients undergoing radical prostatectomy revealed no relationship between the presence of diabetes and the development of more aggressive tumours. Diabetic patients had significantly higher prostatic volumes, however, no significant difference was found between the relapse risk classification or the ISUP classification between the two groups. Conclusions: Our results showed that medium glucose concentration could influence prostate cancer cells growing but not the aggressiveness.