Although interleukin-25 (IL-25) has been traditionally considered as a cytokine involved in T helper (Th) 2 cell-associated allergic diseases and host defence against helminthic parasites, recent studies have shown that IL-25 exerts negative effects on the initiation and progression of Th1/Th17-mediated pathologies. This later function of IL-25 is particularly evident at the gut level, where IL-25 could contribute to attenuate tissue-damaging immune responses. These new and exciting pre-clinical observations suggest that therapeutic interventions aimed at enhancing IL-25 activity could be useful in the management of patients with chronic gut inflammation.