Using immunohistochemistry, Western blotting, lectin profiling, histochemical staining, and transcriptomic analysis, we compared mucin levels and glycosylation patterns in eutopic and ectopic tissues from women with and without endometriosis and measured mucin-derived tumor markers in serum (CA 125/MUC16 and CA 15-3/MUC1) and peritoneal fluid (CA 125/MUC16). Here, MUC1 is linked to endometriosis.