The acceptance of paternally-derived alloantigens during pregnancy and escape from host immunosurveillance by cancer are based on similar immunological mechanisms. Among them both natural and peripherally-induced T CD4+ CD25+ Foxp3+ and Tr1 regulatory cells (Tregs) play important role. Interactions of Tregs with other immunocytes including dendritic cells, mechanisms of Tregs recruitment and their suppressive properties in cancer and pregnancy have been presented in this paper. Despite the fact that mechanisms of Treg regulation are still in progress, there is a hope for use of Tregs-related immunotherapy in clinical practice, and the first attempts of such management have already been described. However, more information about the function of Tregs cells is needed to provide safe treatment devoid of potential side-effects. Resolving the secrets of Tregs cells will probably offer new options of cancer treatment and will help to improve the management of pregnancy failure.