The "neighborhood effects" literature, as currently constructed in epidemiology, would benefit from critical attention to the following four issues: 1) use of appropriate measurement tools and methods for neighborhood environments; 2) theoretical or conceptual guidance as to the aspects of residential environments most salient to human health (both within and across health endpoints); 3) the scale on which investigators measure neighborhood environments to best correspond to meaningful neighborhood boundaries and relevant neighborhood exposures; and 4) those selection and structural features that confound investigators' capacity to draw causal inferences from neighborhood environments to human health. In this issue of the Journal, Mujahid et al. (Am J Epidemiol 2007;165:858-867) report on the psychometric and ecometric results of their neighborhood scale testing. By providing a more rigorous approach to testing of neighborhood-attribute measurement tools, they make an important contribution to the literature. Also noteworthy is their explicit use of a conceptual model, which may facilitate the development of more meaningful area-level measures. Unfortunately, while Mujahid et al. had the capacity to consider spatially relevant measures, based on prior research and their conceptual model, they relied exclusively on aggregated census units. Hopefully, the scale issue will be addressed more thoroughly in future work. Clearly, Mujahid et al. have made progress in addressing how, and to a lesser extent what, to measure when researchers estimate neighborhood effects. But equally clearly, important work remains to be done.