Diseases know no borders, a truism that largely has been applied to infectious diseases. The re-emergence of tuberculosis, the spread of dengue and malaria, and recent outbreaks of swine and avian influenza remind officials in neighboring countries, as well as throughout shared hemispheres and the world at large, that public health efforts must be concentrated and coordinated. The obesity epidemic, like the cigarette smoking epidemic before it, is a chronic disease–related condition that also knows no boundaries.