In this single-center cohort of women undergoing laparoscopic surgery for endometriosis (EM), higher pre-operative white-blood-cell-to-hemoglobin ratio (WHR)—a composite reflecting systemic inflammation (WBC) and anemia/oxygen-carrying capacity (Hb)—was associated with lower postoperative health-related quality of life (HRQoL) at 3 months, particularly the Physical Component Summary (PCS) and the domains of physical functioning, role-physical, vitality and role-emotional, after covariate adjustment. This evidence concerns the gene GSTM1 and anemia (phenotype).