Older people constitute a growing proportion of the urban population and are encountered in all kinds of spaces and neighbourhoods across cities. This article argues that urban seniority and elderly care are a fruitful, new lens to study how inhabitants on the social margins create urban space and social cohesion. This article draws on ethnographic research in the cities of Zanzibar, Tanzania, and Muscat, the capital of Oman. Many older inhabitants of cities experience frailty, serious health problems, or even disabilities and are no longer able to work or make a living, which pushes them towards the social margins. The ethnographic examples and reflections in this article illustrate, first, how cities can be investigated from the perspective of social and spatial marginality. Second, they show how urban dwellers' social positions can shift between the margins and centres of an urban society depending on their health and access to unequal spaces of ageing and care. And third, the paper analyses how some elders respond to marginality by taking up transnational and cosmopolitan agency.