Background. Obese adults are frequently vitamin D deficient before bariatric surgery; whether similar abnormalities exist in morbidly obese adolescents is unknown. Objective. To determine the prevalence of vitamin D deficiency in morbidly obese adolescents. Methods. Cross-sectional study of preoperative laboratory measures from 236 adolescents evaluated for bariatric surgery. Results. The group ( with 25-hydroxyvitamin D (25OHD) and parathyroid hormone (PTH) levels; 76 boys, 143 girls; years; 43% Caucasian, 35% Hispanic, and 15% African American) had mean BMI of kg/m2. 25OHD levels were deficient (<20 ng/mL) in 53%; 8% had severe deficiency (<10 ng/mL); only 18% of patients were replete (>30 ng/mL). 25OHD levels were inversely associated with BMI ( , ) and PTH levels ( , ). Race was the strongest predictor of 25OHD ( ); 82% of African Americans, 59% of Hispanics, and 37% of Caucasians were deficient. African American race, BMI, and PTH explained 21% of the variance in 25OHD ( ). Conclusions. Most adolescents presenting for bariatric surgery have suboptimal vitamin D levels, with African Americans and those with higher BMIs at greatest risk for vitamin D deficiency. All morbidly obese adolescents should be screened for vitamin D deficiency before bariatric procedures.