Francisella tularensis, the causative agent of tularemia, infects host macrophages, which triggers production of the proinflammatory cytokines interleukin 1beta (IL-1beta) and IL-18. We elucidate here how host macrophages recognize F. tularensis and elicit this proinflammatory response. Using mice deficient in the DNA-sensing inflammasome component AIM2, we demonstrate here that AIM2 is required for sensing F. tularensis. AIM2-deficient mice were extremely susceptible to F. tularensis infection, with greater mortality and bacterial burden than that of wild-type mice. Caspase-1 activation, IL-1beta secretion and cell death were absent in Aim2(-/-) macrophages in response to F. tularensis infection or the presence of cytoplasmic DNA. Our study identifies AIM2 as a crucial sensor of F. tularensis infection and provides genetic proof of its critical role in host innate immunity to intracellular pathogens.