Here we report on the association between prostate cancer and the gene encoding 17β-hydroxysteroid dehydrogenase 1 (17β-HSD-1), HSD17B1, which is situated on chromosome 17q21 near BRCA1. 17β-HSD-1 plays a role in estrogen and testosterone biosynthesis. This evidence concerns the gene BRCA1 and Familial prostate cancer.