OBJECTIVE The aim of this study was to evaluate the influence of serum 25-hydroxyvitamin D [25(OH)D] levels at birth in postnatal growth at discharge and 12 mo of corrected age in preterm infants. METHODS This prospective cohort included 63 preterm newborns born before 34 gestational weeks evaluated from birth until 12 mo of corrected age. The serum 25(OH)D levels in umbilical cord blood and from their mothers were evaluated at delivery. RESULTS The mean 25(OH)D levels in preterm newborns were higher than maternal levels (24.8 ± 13.3 ng/mL versus 21 ± 10.2 ng/mL, P < 0.001) and showed a moderate correlation between (r = 0.548; P < 0.001). Considering the body mass index Z-score at 12 mo, 3 (10%), 25 (83%), and 2 (7%) of the preterm infants were thin, had normal body mass index, and were overweight, respectively. The 25(OH)D levels in the umbilical cord did not influence the anthropometric indicators at hospital discharge and 12 mo of corrected age. We observed improvement in all anthropometric indicators assessed over the months, and there was no difference between preterm infants with 25(OH)D levels >20 ng/mL and <20 ng/mL in the umbilical cord. CONCLUSIONS The results of this study suggested that the 25(OH)D serum levels in the umbilical cord did not influence postnatal growth from birth to the first year of life in preterm infants. There was a direct association between maternal and umbilical cord serum 25(OH)D levels.