The aims of this article are to assess the quality of the indoor living environment of a senior housing (rental apartments for older adults aged 65+) in Hässelgården, Stockholm Municipality (Sweden's capital), in 2014, in relation to their mobility, and to suggest improvement strategies. First, the physical indoor environment of older adults is examined via a fieldwork checklist devised in accordance with the principles of universal design (UD). Second, their indoor environment is assessed through a survey that includes subjective questions about seniors' use of space, experience of falls, and safety perception. Third, the study explores whether the applications of UD in the seniors' indoor living environment contribute to the understanding of their use of space, experience of falls, and safety perception. Fieldwork inspections and a detailed survey with residents are used as a basis for the empirical analysis. Overall, 27 out of 56 questionnaires were collected, and ten apartments have been visited in the fieldwork. Findings indicate that the living room has the highest UD score compared with those for the kitchen and the bedroom. The older adults spend most of their time in the living room and the kitchen. A low UD score (e.g. kitchen and bedroom) is associated with a higher number of falls but not with low levels of safety perception and use of space. The article concludes with suggestions to improve housing safety of Hässelgården's senior housing, which may also help prevent falls in the older population elsewhere.