Ovarian cancer is the most lethal gynecological malignancy in the western world. Although patients with early-stage ovarian cancer generally have a good prognosis, approximately 20%-30% of patients will die of the disease, and 5-year recurrence rates are 25%-45%, highlighting the need for improved detection and treatment. We investigated the role of VAV1, a protein with guanine nucleotide exchange factor activity, which is associated with survival in patients with early-stage ovarian cancer (International of Obstetrics and Gynecology [FIGO] stages I and II). We analyzed 88 samples from patients with primary epithelial ovarian cancer, which were divided into FIGO stages I and II (n = 46), and III and IV (n = 42). Prognostic analysis revealed that upregulated VAV1 expression correlated significantly with poor prognosis in patients with early-stage epithelial ovarian cancer (P ≤ 0.05), but not with other clinicopathologic features. Stable overexpression of VAV1 in human high-grade serous ovarian cancer SKOV3 cells induced morphologic changes indicative of loss of intercellular adhesions and organized actin stress fibers. Western blotting and real-time reverse transcriptase-polymerase chain reaction demonstrated that these cells had downregulated E-cadherin protein and messenger RNA levels, respectively. This downregulation is associated with epithelial-mesenchymal transition (EMT) and invasive cancer. Furthermore, VAV1 overexpression in both SKOV3 and human ovarian surface epithelial cells demonstrated that its upregulation of an E-cadherin transcriptional repressor, Snail and Slug, was not confined to ovarian cancer cells. Conversely, knockdown of VAV1 by RNA interference reduced Snail and Slug. Our findings suggest that VAV1 may play a role in the EMT of ovarian cancer, and may serve as a potential therapeutic target. Copyright © 2013 Mosby, Inc. All rights reserved.