OBJECTIVE: To evaluate the presence of Fusobacterium spp. and Fusobacterium nucleatum in eutopic endometrial samples from women with endometriosis compared with controls, and assess their association with the disease. DESIGN: Retrospective case-control study. SUBJECTS: Ninety-two women (55 endometriosis cases and 37 controls) aged 18-44 years undergoing gynecologic endoscopy for endometriosis and/or benign conditions at University of Pennsylvania, Endomarker Study (PMID: 29524590). EXPOSURE: DNA extraction from eutopic endometrial samples using QIAamp DNA Microbiome and IndiSpin Pathogen Kits. Quantification of Fusobacterium spp. and F. nucleatum by quantitative PCR using genus- and species-specific primers. MAIN OUTCOME MEASURE(S): Relative abundance of Fusobacterium spp. and F. nucleatum in cases vs. controls, analyzed using the ΔCt method. RESULTS: No significant difference in Fusobacterium spp. or F. nucleatum abundance was observed between cases and controls (P = .258 for genus-specific primers, P = .738 for species-specific primers). Subgroup analysis by disease severity (minimal-mild: n = 42; moderate-severe: n = 13) also showed no significant differences (Fusobacterium spp.: P = .1465; F. nucleatum: P = .2936). CONCLUSION: Fusobacterium spp. is not differentially present in eutopic endometrium of women with endometriosis, regardless of disease severity according to revised American Society for Reproductive Medicine classification. This contrasts with prior findings in eutopic endometrium in patients with ovarian endometriosis, suggesting that Fusobacterium has limited diagnostic or prognostic value in endometriosis.