Epidemiologists and social scientists agree that place shapes health. But the model of "risk factor" epidemiology faces limits in explaining how neighborhoods, as complex systems, produce health or disease. This paper describes how visual methods can advance epidemiological inquiry. Drawing from the work of The Health of Philadelphia Photo-documentation Project (HOPPP), this paper asks the following question: how can visual methods inform the work of epidemiologists? The project was conducted in three contiguous neighborhoods that represent a steep socioeconomic gradient. Photographs served as a stimulus for probing the sources of health variation across neighborhoods. The project incorporated three visual data sources: 1) "outsider perspective" images gathered systematically by staff photographers on randomly sampled blocks; 2) "insider perspective" images taken by adult residents during their daily routines; and 3) collaborative images taken by staff photographers in partnership with local participants. During in-depth interviews, these photographs served as prompts to elicit residents' health concerns and beliefs regarding urban environmental causes of good and poor health ("street-level etiologies"). We found that visual methods generated etiologic insights regarding the production of urban health and illness. Photographs enabled systematic observation of urban neighborhoods by the research team; engaged urban residents as active agents in the search for the underlying causes of urban health disparities; and created a social bridge between researchers and urban residents.