T helper 17 (TH17) cells have been identified as a new lineage of helper T cells and have been shown to be important in host defense against extracellular infectious agents, autoimmune disease and chronic inflammatory diseases. Recently, TH17 cells have also been shown to participate in successful pregnancy, as well as in the pathogenesis of diseases of pregnancy, such as recurrent spontaneous abortion (RSA) and pre-eclampsia (PE). Here, we review our current knowledge of TH17 cells in human RSA and PE. We also discuss how the local uterine microenvironment affects the differentiation of TH17 cells and the mechanisms that regulate TH17 cells during pregnancy. Research into TH17 cells will not only advance our understanding of TH17-related pregnancy complications, but will also facilitate the design of novel therapies for reproductive diseases.