Mesenchymal stem cells (MSC) are widely studied for their immunomodulatory properties. Data from in vitro and pre-clinical models demonstrate that MSC suppress activated immune cells and ameliorate the severity of experimental immune disease. In complex human studies, the immunomodulatory efficacy of MSC therapy is not well established. We conducted a systematic review of clinical studies which used MSC with the purpose of immunomodulation and included at least 10 patients to investigate the efficacy of MSC therapy. Sixty-two studies comprising 10 different immune disorders were included in the analysis, of which 18 studies represented controlled trials. Although several of the studies reported an amelioration of disease severity, other studies failed to observe a beneficial effect of MSC. The low number of randomized controlled trials, small number of studies per disease category and limited immunological readout parameters made it difficult to draw a definitive conclusion on the efficacy of MSC immune therapy.