Regulatory T cells (Treg), also termed suppressor T cells, control self-reactive T cells in the periphery, thereby conferring protection against immunologic self-destruction. While Treg are essential for the prevention of autoimmunity, they also inhibit immune responses against tumor antigens. This is corroborated by an increased mortality rate associated with the presence of a high number of intratumoral Treg. Tumor infiltration by non-Treg, on the other hand, is predictive for a substantially longer patient survival. These clinical data suggest that ovarian cancer patients can spontaneously mount effective antitumor immune responses that are undermined by Treg-mediated tolerization. The present article reviews clinical and experimental findings on Treg in ovarian cancer, with special regard to potential therapeutic implications, which may result from the existing evidence.