Stenosing tenosynovitis of the first dorsal compartment of the wrist (a.k.a. de Quervain's disease) is common but how estrogen is involved is still unknown. We previously reported that inflammation was involved in the pathogenesis of this ailment. In the present study, we extended our investigation of estrogen receptor (ER)- expression to determine whether estrogen is involved in the pathogenesis of de Quervain's. Intraoperative retinaculum samples were collected from 16 patients with the ailment. Specimens were histologically graded by collagen structure and immunohistochemically evaluated by quantifying the expression of ER-, interleukin (IL)-1 and IL-6 (inflammatory cytokines), cyclooxygenase (COX)-2 (an inflammatory enzyme), and vascular endothelial growth factor (VEGF), and Von Willebrand's factor (vWF). De Quervain's occurs primarily in women. The female:male ratio in our study was 7:1. We found that ER- expression in the retinaculum was positively correlated with disease grade and patient age. Additionally, disease severity was associated with inflammatory factorsIL-1 and IL-6, COX-2, and VEGF and vWF in tenosynovial tissue. The greater the levels of ER- expression, tissue inflammation, and angiogenesis are, the more severe de Quervain's disease is. ER- might be a useful target for novel de Quervain's disease therapy.