OBJECTIVES: To estimate the efficacy of vitamin D supplementation to reduce urgency urinary incontinence (UUI) episodes. DESIGN: Pilot, two-arm, randomized trial conducted from 2013 to 2017. Interventions were 12 weeks of weekly oral 50,000 IU vitamin D3 or placebo. SETTING: Academic, university-based outpatient clinic. PARTICIPANTS: Community-dwelling postmenopausal women, 50 years or older, with at least three UUI episodes on 7-day bladder diary and serum vitamin 25-hydroxyvitamin D (25[OH]D) of 30 ng/mL or less. MEASUREMENTS: The primary efficacy estimate was the percentage change in UUI episodes. Secondary estimates included changes in other lower urinary tract symptoms, along with exploratory subgroup analysis by race/ethnicity and obesity. RESULTS: We randomized 56 women (aged 50-84 years; mean = 60.5 ± 8.2 years), 28 to vitamin D and 28 to placebo; 51 completed treatments. Mean serum 25(OH)D at baseline (21.2 ± 5.2 and 18.2 ± 5.6, P = .30) improved to 57.9 ± 16.3 ng/mL with vitamin D3 and 21.9 ± 8.2 ng/mL with placebo (P < .001). UUI episodes per 24-hour day decreased by 43.0% with vitamin D3 compared to 27.6% with placebo (P = .22). Among black women (n = 33), UUI episodes decreased by 63.2% with vitamin D3 compared to 22.9% with placebo (P = .03). Among obese women, UUI episodes decreased by 54.1% with vitamin D compared to 32.7% with placebo (P = .29). For all women, changes in voiding frequency (P = .40), nocturia (P = .40), urgency (P = .90), incontinence severity (P = .81), and overactive bladder symptom severity (P = .47) were not different between arms. CONCLUSIONS: Postmenopausal women with UUI and vitamin D insufficiency demonstrated a greater than 40% decrease in UUI episodes, which did not reach statistical significance compared to placebo, except in the subset of black women. The results of this pilot study support further investigation of vitamin D3 alone or in combination with other treatments for UUI, particularly for women in higher-risk subgroups.