Recent work by Muraoka and colleagues reports that the Gram-negative anaerobic bacterium Fusobacterium nucleatum is detected in the uterus of 64% of women with endometriosis. Fusobacterium infection causes macrophage infiltration, transforming growth factor-β production, and transgelin upregulation in human and mouse endometria as well as endometriotic lesion development in a mouse model of endometriosis.