Background: The HSD3B1(1245A > C) variant allele, whose frequency varies by race, encodes a missense sequence that stabilizes the rate-limiting enzyme responsible for extragonadal androgen synthesis, thus enhancing intratumoral dihydrotestosterone (DHT) synthesis. Multiple retrospective studies have found that men inheriting the HSD3B1(1245C) variant allele exhibit early resistance to ADT. We sought to validate these findings with prospective data from the Chemohormonal Therapy versus Androgen Ablation Randomized Trial for Extensive Disease in Prostate Cancer (CHAARTED). Methods: Men with newly metastatic PCa were randomized to receive either ADT plus docetaxel at a dose of 75 mg/m² every 3 weeks for 6 cycles (arm A) or ADT alone (arm B). We determined germline HSD3B1 genotype in the subset of men with LV disease ( < 4 bone metastases, no visceral metastases). We analyzed freedom from castration-resistant prostate cancer (CRPC) and OS according to HSD3B1 genotype using Cox and Kaplan-Meier methods. Results: 197 patients with LV disease had blood samples available and were genotyped, including 97 in arm A and 100 in arm B. Docetaxel did not improve OS of LV men. Of the 197 men, 47% were homozygous wild-type (WT), 43% were heterozygous, and 10% were homozygous variant. When all 197 men were analyzed as one goup, the median time to CRPC was 39.7 mos. in homozygous WT men vs. 25.0 mos. in men with one or more copies of the variant allele (HR 1.27, 95% CI 0.89 to 1.82; p = 0.187). Although OS data are still maturing, at 52 months OS was 83% (95% CI 75% to 91%) in homozygous WT men vs. 64% (95% CI 55% to 74%) in men with one or more variant alleles. There was a suggestion that docetaxel delayed development of CRPC among men with at least 1 variant allele (20.3 vs. 40.7 mos.; HR 0.66, 95% CI 0.40 to 1.04; p = 0.08). Benefit for men with high-volume disease was not evident. Conclusions: Inheritance of the HSD3B1(1245C) allele that augments DHT synthesis may be associated with lower OS in men treated with ADT with or without docetaxel for LV newly metastatic PCa. Additional study is warranted in patients with LV disease. Clinical trial information: NCT00309985