Background: The NLR is a marker of systemic inflammatory response: several studies investigated its prognostic relevance in mCRPC but to date no information is available concerning this issue in pts treated in third line therapy. The present study is aimed to assess the possible relationship between third line clinical outcome and NLR in a large series of mCRPC pts treated with a NA [abiraterone acetate (AA), cabazitaxel (CABA), or enzalutamide (ENZ)] after the failure of docetaxel (DOC) and another NA. Methods: We collected data of pts who received sequentially two NAs after DOC in 38 Italian hospitals. For each pt we recorded the clinical outcome of all treatments received after DOC. Cox regression analysis was used to assess the independent prognostic value of a series of pretreatment covariates, in terms of overall survival (OS), comprising NLR. Results: A consecutive series of 291 mCRPC pts with bone (88%), nodal (53%) or visceral (18%) mets, was collected. All pts received a NA-based third line: 90 received AA, 123 CABA and 78 ENZ. At the time of this analysis, data on NLR were available for 198 pts (68%): AA 68 (75%) – CABA 80 (65%) – ENZ 50 (64%): the median value was 3.1 (IQR 2.2-4.7). In the univariate analyses, the NLR as a discrete variable using the median value of 3.1 as threshold, was significantly associated with both OS and progression free survival (PFS), calculated from the third line start (p < 0.0001 and p = 0.001, respectively). No association was observed with either biochemical or objective response. These results were confirmed at the multivariate analysis. In Kaplan-Meier analysis, the median OS from the start of third-line was higher (18.2 vs 8.1 mos) in pts with NLR ≤ 3.1 compared to those with NLR > 3.1 (log-rank; P < 0.0001). Similarly, the median PFS was 6.3 and 3.5 in pts with NLR ≤ 3.1 and > 3.1, respectively. Conclusions: At the best of our knowledge, this is the first report on the NLR value in mCRPC third line treatment. From our preliminary data, it appears that NLR may be a prognostic and predictive factor in mCRPC pts, treated with NA-based third line.