Ovarian serous borderline tumors (SBTs) are presumed to originate in the ovarian cortex or peritoneal surface. The pathogenetic role of the fallopian tube (FT) is unclear; however, recently, secretory cell outgrowths (SCOUTs) lacking PAX2 expression were described in benign FTs. This study addressed (1) the differentiation characteristics of SBTs and (2) the frequency of SCOUTs lacking PAX2 expression in the FTs of patients with SBTs and compared (3) SCOUT morphology and (4) PAX2 expression with SBTs. SBTs and FT epithelium shared both ciliated (p73) and secretory (HMFG2) differentiation. PAX2-null SCOUT frequency in FT cross-sections from patients with SBTs was 0.28 (110 of 398) versus 0.112 in benign hysterectomies and nearly 0 in pediatric and postpartum sterilization specimens (P = < 0.001). When adjusted for age, the differences narrowed but remained significant (P = 0.010). SCOUTs were heterogeneous, some displaying ciliated differentiation and papillary architecture. Two cases of discrete multifocal papillary SCOUTs in the FTs were associated with SBTs. All SBTs had heterogeneous PAX2 staining with areas of PAX2 loss. This study shows for the first time that PAX2-null SCOUTs are more common in the oviducts of women with SBTs and that loss of PAX2 expression occurs in most SBTs. These discoveries link both morphologic and functional gene (PAX2) alterations in the oviduct to SBTs, similar to that reported in high-grade serous carcinoma. Further study is warranted to clarify the relationship of the oviduct to serous neoplasia.