BACKGROUND: Climate change is expected to disrupt weather patterns across the world, exposing older adults to more intense and frequent periods of hot weather. Meanwhile, lab-based studies have established a causal relationship between ambient temperature and cognitive abilities, suggesting the expected rise in temperature may influence older adults' cognitive functioning. Nevertheless, it is not clear whether, and to what extent, the temperature variations in older adults' own homes-which unlike lab settings are under their control-influence their cognitive functioning. Our objective was to provide proof of concept that home ambient temperature influences self-reported ability to maintain attention in older adults. METHODS: We conducted a longitudinal observational study, continuously monitoring the home ambient temperature and self-reported difficulty keeping attention for 12 months in 47 of community-dwelling older adults living in Boston, Massachusetts. RESULTS: We observed a U-shaped relationship between home ambient temperature at the time of assessment and the odds ratio (OR) of reporting difficulty keeping attention such that the OR was lowest between 20°C and 24°C and doubled when moving away from this range by 4°C in either direction. DISCUSSION: Our results suggest that even under the current climate, a considerable portion of older adults encounter indoor temperatures detrimental to their cognitive abilities. Climate change may exacerbate this problem, particularly among low-income and underserved older adults. Addressing this issue in public health and housing policy is essential to building climate resiliency in this vulnerable population.