BACKGROUND: Decision-making and selection of treatment modalities for newly diagnosed prostate cancer (PCa) are often determined by risk stratification using grade group (GG), prostate-specific antigen (PSA), and clinical stage. The discrepancies between needle biopsy (NB) and radical prostatectomy (RP) specimens often occur because of the sampling errors in NB or multifocal features of PCa. Thus, we aimed to estimate the preoperative clinical factors for predicting GG upgrading after robot-assisted RP (RARP). METHODS: In this retrospective study, we reviewed the clinical and pathological records of patients who underwent RARP at Gifu University Hospital. We focused on patients with organ-confined PCa who had not received neoadjuvant therapy prior to RARP. The primary endpoint was identified as the predictive factor of GG upgrading for RARP specimens compared to those of NB specimens. RESULTS: Eighty-one patients were included in this study. The enrolled patients were divided into two groups: those who had GG upgrading for RARP specimens (the NB upgrade group) or those who did not have GG upgrading (the no upgrade group). The median age of all patients was 70 years, and the median body mass index (BMI) was 22.9 kg/m2. The median neutrophil count was 3720/μL, lymphocyte count was 1543/μL, and neutrophil-to-lymphocyte ratio (NLR) was 2.24. In univariate analysis, BMI, PSA, neutrophil count, and NLR were significantly associated with GG upgrading in RARP specimens compared to NB specimens. BMI and NLR were identified as strong predictive factors for GG upgrading in RARP specimens in the multivariate analysis. CONCLUSIONS: Although this study's small number of enrolled patients was a vital weakness, BMI and NLR might have been significantly correlated with GG upgrading for RP specimens compared with NB specimens. Therefore, BMI and NLR may have potential benefits for newly diagnosed patients with PCa in terms of decision-making and the selection of treatment modalities.