Abstract The purposes of this paper are: to describe an ecological approach to assessing health risk, and to apply the approach to a sample of elderly homeless within the context of a single day in a single urban setting. In the approach described, a method of progressive contextualization was used by adding different hazards to the risk profile in a single geographic area. The various hazards were applied to the same time and space frame, that of a 24-hour period and in the urban space used by elderly homeless people. Incorporated into the approach are the concepts of high-risk areas and space-time geography, and the theory of disease ecology. The spatial-temporal distribution of resources, factors in the natural environment (patterns of daylight and dark and ambient temperature) and factors in the human-created environment (traffic and crime patterns) were identified as important hazards within the urban environment. Homelessness itself, the effects of aging, the social milieu, and behavior patterns commonly seen in homeless people—particularly, alcohol abuse-were identified as important hazards for elderly homeless people. Each hazard's spatial-temporal pattern within the 24-hour period is discussed. Then the convergence of hazards forming an interactive effect is discussed. Finally, approaches to nursing interventions aimed at reducing risk are presented.