Abstract Context The Study to Understand Fall Reduction and Vitamin D in You (STURDY), a randomized trial enrolling older adults with low 25-hydroxyvitamin D [25(OH)D], demonstrated vitamin D supplementation ≥ 1000 IU/day did not prevent falls compared with 200 IU/day, with doses ≥ 2000 IU/day potentially showing safety concerns. Objective To examine associations of achieved and change in 25(OH)D concentrations after 3 months of vitamin D supplementation with fall risk. Design Observational analysis of trial data. Setting General community. Participants A total of 637 adults aged ≥ 70 with baseline 25(OH)D concentrations 10 to 29 ng/mL and elevated fall risk. Three-month on-treatment absolute 25(OH)D; absolute and relative changes from baseline. Main Outcome Measures Incident first fall (primary) and first consequential fall (injury or sought medical care) up to 24 months. Cox models were adjusted for sociodemographics, season, Short Physical Performance Battery, and body mass index. Results At baseline, mean (SD) age was 77.1 (5.4) years and 25(OH)D was 22.1 (5.1) ng/mL; 43.0% were women and 21.5% non-White. A total of 395 participants experienced ≥ 1 fall; 294 experienced ≥ 1 consequential fall. There was no association between absolute achieved 25(OH)D and incident first fall (30-39 vs < 30 ng/mL hazard ratio [HR], 0.93; 95% CI, 0.74-1.16; ≥40 vs < 30 ng/mL HR, 1.09; 95% CI, 0.82-1.46; adjusted overall P = 0.67), nor absolute or relative change in 25(OH)D. For incident consequential first fall, the HR (95% CI) comparing absolute 25(OH)D ≥ 40 vs < 30 ng/mL was 1.38 (0.99-1.90). Conclusion Achieved 25(OH)D concentration after supplementation was not associated with reduction in falls. Risk of consequential falls may be increased with achieved concentrations ≥ 40 ng/mL. Trial Registration ClinicalTrials.gov: NCT02166333