Among 61 individual proteins nominally significantly associated with risk of endometriosis diagnosis compared to controls, endometriosis cases had higher plasma levels of S100A9 (OR = 1.52, 95%CI = 1.19–1.94), ICAM2 (OR = 1.47, 95%CI = 1.17–1.85), HIST1H3A (OR = 1.42, 95%CI = 1.31–1.78), TOP1 (OR = 1.95, 95%CI = 1.24–3.06), CD5L (OR = 1.23, 95%CI = 1.00–1.51) and lower levels of IGFBP1 (OR = 0.70, 95%CI = 0.52–0.94). This evidence concerns the gene CD5L and endometriosis.