Background: Recent studies have shown that vitamin D status may be relevant for physical and cognitive performance in the older population. This association may be of particular interest to older people at risk for cognitive impairment and functional decline. Objective: The aim of this study was to determine the association between serum 25-hydroxyvitamin D [25(OH)D] status and functional mobility in seniors assessed in a memory clinic. Methods: We conducted a cross-sectional study of outpatients (n = 404) in a memory clinic. Functional mobility was assessed with three endpoints: normal and fast walking speed and the Timed Up and Go (TUG) test. Adjusted multivariate analyses in all patients and two pre-planned subgroup analyses in vulnerable seniors (previous fall and MMSE score of ≥26 or no previous fall and MMSE score of <26) versus less vulnerable seniors (no previous fall and MMSE score of ≥26) were performed to assess the association of 25(OH)D and functional mobility. Results: Overall, mean 25(OH)D serum levels were 63.2 ± 33.9 nmol/l, and 41.3% were vitamin D deficient (<50 nmol/l). Seniors in the lowest 25(OH)D quartile (<39 nmol/l) had significantly worse functional mobility compared to the highest 25(OH)D quartile (>81 nmol/l); adjusted for all covariates, seniors in the highest quartile performed 9.4% better in normal (p = 0.02) and 9.2% better in fast (p = 0.004) walking speed, and 4.4% better in the TUG test (p = 0.24). The association between 25(OH)D status and functional mobility was most pronounced in less vulnerable seniors (p for trend significant for all three mobility tests). Seniors with a higher 25(OH)D status also had better cognitive function (MMSE score; p = 0.006). Conclusions: Lower serum 25(OH)D status is associated with poorer functional mobility and cognitive function, therefore supporting 25(OH)D assessment in this population at risk for both functional and cognitive decline. © 2013 S. Karger AG, Basel.