Epidemiological studies suggest that autoimmune diseases, such as multiple sclerosis (MS), are less frequent in individuals who are helminth carriers. This observation has been tested in murine models of colitis, MS, type 1 diabetes and asthma. In each case, mice colonized with helminths show protection from disease. This apparent down-modulation of inflammatory response resulting from helminth infection has triggered interest in exploring the potential clinical efficacy of controlled helminth infection in patients suffering from autoimmune diseases. To date, clinical trials using helminth therapy (Trichura suis ova [TSO] or Necator americanus larvae) in MS have been small, safety-oriented trials of short duration, attempting to reproduce and confirm epidemiological and experimental data. Thus far, no adverse events related to therapeutic helminth infection have been observed. Nonetheless, there is a clear need for caution when considering such approaches. Some preliminary clinical, magnetic resonance imaging and immunological outcomes using TSO have been encouraging. Nevertheless, results should be interpreted with caution as the number of individuals studied was small and duration of follow up limited. Longer studies, monitoring safety and objective outcome measures are necessary to assess this novel therapeutic strategy in a more definitive fashion. An alternative approach to use of live helminth infections might arise from identification of helminth-derived immunomodulatory molecules mimicking the protective effects of parasite infection, i.e. capable of altering immune responses and, therefore, the course of autoimmune diseases. Although positive results from administering parasite products in mouse models of autoimmunity have been reported, much remains to be explored before the field can move from experimental animal models to application in clinical practice. To the best of my knowledge, parasite-derived molecules have not yet been administered as treatment for any autoimmune disease in humans. At this time, it is strongly recommended that live helminth or ova parasites be administered only to individuals participating in strictly monitored, controlled clinical trials.