The Rho GDP dissociation inhibitors (RhoGDIs) are a major class of regulators of Rho GTPases and play essential roles in normal cell growth and malignant transformation. Although RhoGDIs are known to inhibit Rho activities, recent studies indicate that RhoGDIs can also act as positive regulators through their ability to target Rho GTPases to specific subcellular membranes or to protect the GTPases from degradation by caspases. RhoGDIs are aberrantly expressed in human tumors and this may contribute to Rho-induced cancer progression. This review will discuss the dual roles of RhoGDIs in the regulation of Rho GTPases, highlighting a possible role in regulating tumorigenicity. In addition, the potential for targeting RhoGDIs for anticancer therapy will be discussed.