Background: Previous research suggests that HRR mutations may have prognostic value in mCRPC. Additionally, HRR mutations are therapeutically relevant and can inform treatment decisions. Limited information is available on HRR mutation testing rates in the US. This study assessed rw HRR testing patterns in pts with mCRPC in the US and described characteristics associated with HRR testing. Methods: Retrospective data from pts with mCRPC initiating first line (1L) treatment between 2014 – 2021 was obtained from the nationwide Flatiron Health electronic health record-derived de-identified database. Pt demographic and clinical characteristics were summarized descriptively across subgroups by HRR gene testing status (tested vs not tested). A multivariable logistic regression model was used to assess factors associated with receiving HRR testing, and included covariates for demographic, clinical, and treatment characteristics. Results: A total of n=8,166 pts with mCRPC receiving 1L treatment were identified. The mean age of the cohort was 72.9 (standard deviation (SD) 8.1) years. Overall, 2,122/8,166 (26%) were known to have received HRR mutation testing. Pts who did not receive HRR testing were older compared to HRR tested pts (mean age 73.7 (SD 8.5) vs 70.6 (SD 7.5) years). A higher proportion of HRR tested were receiving treatments from an academic medical center vs community practice (14.5% vs. 7.7%). Multivariable logistic regression indicated age > 65 (vs < 65 years), Black race (vs White), being treated in the community (vs academic), and having de novo metastatic disease (vs recurrent) were associated with a statistically significant lower odds of HRR mutation testing. In contrast, a higher socioeconomic status and being diagnosed with mCRPC after 2018 were associated with a statistically significant increased odds of HRR mutation testing. Conclusions: In this rw study, a minority of US pts with mCRPC received HRR mutation testing. Disparities in HRR mutation testing exist, and focused efforts to increase HRR testing should be developed, especially among Black pts, pts with lower socioeconomic status, pts treated in the community setting, and pts > 65 years of age.