The incidence of the inflammatory bowel diseases (IBD) ulcerative colitis (UC) and Crohn′s disease (CD) markedly increased in industrialised countries during the past decades. In contrast to these countries where helminthosis are rare, IBD is still uncommon in global areas where most people carry worms. Thus lack of exposure to parasites may critically contribute to the risk of IBD. In a recent article in Gut, Summers et al. demonstrated efficacy of treatment with Trichuris suis in active CD (Gut 2005;54:87-90). Trichuris suis was additionally shown to be effective in UC in a randomized trial carried out by the same group. Both studies did not address mechanisms of action. Here we present a real life scenario, which supports the impact of helminths in the prevention of IBD, and provide a rationale for the mechanisms of action.