Objective: Outdoor mobility is critical for healthy aging, yet little is known about the factors influencing mobility in the frail elderly. We investigated the role of individual and community risk factors on trajectories of mobility in a population of vulnerable community-dwelling elderly. Method: Using data from 1,188 older adults in Detroit, MI, who qualify for federally funded home care, a latent class growth analysis was used to model the frequency of going outside over a 15-month period. Results: Four latent trajectories were found: those with a low, high, and declining frequency of going outdoors over time, and those who do not go outdoors on a regular basis. Risk factors for membership in the homebound and infrequent mobility groups were older age, more severe mobility impairment, and fear of falling. Barriers at the entry to the home were associated with being homebound. Discussion: Declining health status and functional limitations are risk factors that pose a threat to outdoor mobility in the frail elderly, while housing barriers and community accessibility also merit attention.