OBJECTIVE: The aim of this study was to determine the associations between calcium + vitamin D supplementation (vs placebo) and height loss in 36,282 participants of the Women's Health Initiative Calcium and Vitamin D trial. METHODS: Post hoc analysis of data from a double-blind randomized controlled trial of 1,000 mg of elemental calcium as calcium carbonate with 400 IU of vitamin D3 daily (CaD) or placebo in postmenopausal women at 40 US clinical centers. Height was measured annually (mean follow-up 5.9 y) with a stadiometer. RESULTS: Average height loss was 1.28 mm/y among participants assigned to CaD versus 1.26 mm/y for women assigned to placebo (P = 0.35). Effect modification of the CaD intervention was not observed by age, race/ethnicity, or baseline intake of calcium or vitamin D. Randomization to the CaD group did not reduce the risk of clinical height loss (loss of >/=1.5 inches [3.8 cm]: hazard ratio (95% CI) = 1.00 (0.81, 1.23). A strong association (P < 0.001) was observed between age group and height loss. When we censored follow-up data in participants who became nonadherent to study pills, the results were similar to those of our primary analysis. CONCLUSIONS: Compared with placebo, the CaD supplement used in this trial did not prevent height loss in healthy postmenopausal women.