Loneliness is increasingly understood as a significant physical and mental health concern in modern society. Yet studies of the subject typically characterise it as resulting entirely from subjective individual characteristics and circumstances. The impact of broader living environments is understudied, leaving disciplines such as urban planning with little guidance as to how environmental intervention strategies might best ameliorate loneliness. This paper uses Stockholm as a case study for asking two place-based questions: (1) what can our knowledge of loneliness risk factors tell us about the possible spatial distribution of loneliness in cities? (2) what influence does the built environment itself have on loneliness? An abductive approach is used to test different ways in which urban planners might map risk of loneliness and social isolation in different neighbourhoods. The results shed light on spatial segregation as a potential contributing factor, with implications for planning practice.