Four variants (rs227849, rs4703908, rs2479037, and rs966674) were significantly associated with an increased risk of OMA. Rs4703908, located close to ZNF366, provided a higher risk of OMA (OR = 2.22; 95% CI: 1.26–3.92) and DIE, especially with bowel involvement (OR = 2.09; 95% CI: 1.12–3.91). ZNF366, involved in estrogen metabolism and progression of breast cancer, is a new biologically plausible candidate for endometriosis. This evidence concerns the gene ZNF366 and breast cancer.