CONTEXT: Experimental evidence supports a relevance of vitamin D (VitD) for reproduction; however, data in humans are sparse and inconsistent. OBJECTIVE: To assess the relationship of VitD status with ovulation induction (OI) outcomes in women with polycystic ovary syndrome (PCOS). DESIGN: A retrospective cohort. SETTING: Secondary analysis of randomized controlled trial data. PARTICIPANTS: Participants in the Pregnancy in PCOS I (PPCOS I) randomized controlled trial (n = 540) met the National Institutes of Health diagnostic criteria for PCOS. INTERVENTIONS: Serum 25OHD levels were measured in stored sera. MAIN OUTCOME MEASURES: Primary, live birth (LB); secondary, ovulation and pregnancy loss after OI. RESULTS: Likelihood for LB was reduced by 44% for women if the 25OHD level was < 30 ng/mL (<75 nmol/L; odds ratio [OR], 0.58 [0.35-0.92]). Progressive improvement in the odds for LB was noted at thresholds of ≥38 ng/mL (≥95 nmol/L; OR, 1.42 [1.08-1.8]), ≥40 ng/mL (≥100 nmol/L; OR, 1.51 [1.05-2.17]), and ≥45 ng/mL (≥112.5 nmol/L; OR, 4.46 [1.27-15.72]). On adjusted analyses, VitD status was an independent predictor of LB and ovulation after OI. CONCLUSIONS: In women with PCOS, serum 25OHD was an independent predictor of measures of reproductive success after OI. Our data identify reproductive thresholds for serum 25OHD that are higher than recommended for the nonpregnant population.