To estimate the expression of plasma soluble E-cadherin and the gene polymorphism in patients with pelvic inflammatory disease (PID).Hospital-based case–control study.University hospital.Sixty-four women with PID.Blood specimen collection from patients before and after they received treatment.Enzyme-linked immunosorbent assay and polymerase chain reaction–restriction fragment length polymorphism were respectively used to measure the plasma soluble E-cadherin level and E-cadherin polymorphism.The level of plasma E-cadherin was significantly elevated in patients with PID as compared with that in normal controls; it decreased significantly after treatment when compared with levels noted in the same patients before they received treatment. When the cutoff level of plasma E-cadherin level was set to 20.22 ng/mL on the basis of receiver-operating characteristic curve (ROC), the sensitivity, specificity, and the area under the curve of plasma E-cadherin level for predicting PID were 0.81, 0.80, and 0.835 (95% confidence interval 0.76–0.90), respectively. The adjusted odds ratio for age, white blood cell count, and C-reactive protein levels was 19.66 (5.48–70.47).Elevated plasma soluble E-cadherin expression was involved in the pathogenesis of PID and is useful for the diagnosis of PID.