Objectives: The Women's Health Initiative (WHI) randomized trial of calcium/vitamin D supplementation found reduced bone loss with active treatment compared to placebo. Now we examine whether the treatment affected self-reported physical functioning and objective measures of physical functioning. Design: A randomized, double-blind, placebo-controlled trial of 1,000 mg calcium carbonate plus 400 IU vitamin D3 per day or matching placebo pills. Subjects/setting: The study included 33,067 women (50 to 79 years old) at 40 US study centers. Main outcome measures: Physical functioning was assessed by questionnaire at enrollment in WHI, 1 year prior to calcium/vitamin D trial randomization and at study close-out (average follow-up 7.1 years). Objective physical performance and self-reported exercise measures were collected at WHI baseline (1 year prior to calcium/vitamin D enrollment) and 2 years and 4 years after calcium/vitamin D trial enrollment in a subsample (n=3,137). Statistical analyses performed: Calcium/vitamin D effects were tested in unadjusted and interaction linear models for each of the physical function measures. Covariates were baseline total calcium intake, fracture risk score, treatment arm in the hormone therapy and dietary modification trials (ie, active drug or placebo, low-fat diet intervention or usual diet, respectively) and age. Results: Neither intention to treat nor high adherence analyses produced substantial effects of calcium/vitamin D compared to placebo on physical functioning or performance. The interaction analyses also did not result in differences because of calcium/vitamin D. Conclusions: As the first long-term randomized trial to examine the effectiveness of calcium and vitamin D in protecting against decline of physical functioning in older women, the results did not support benefit. © 2008 American Dietetic Association.