Obesity prevention programs are at last underway or being planned in Australia and New Zealand. However, it is imperative that they are well-evaluated so that they can contribute to continuous program improvement and add much-needed evidence to the international literature on what works and does not work to prevent obesity. Three critical components of program evaluation are especially at risk when the funding comes from service delivery rather than research sources. These are: the need for comparison groups; the need for measured height and weight; and the need for sufficient process and context information. There is an important opportunity to build collaborative mechanisms across community-based obesity prevention sites to enhance the program and evaluation quality and to accelerate knowledge translation into practice and policy.