We analyzed the characteristics of young infants diagnosed with vitamin D deficiency in early infancy at 2 medical centers in Turkey. In this retrospective, cross-sectional study, the clinical, biochemical, and radiographic findings of infants who were diagnosed with vitamin D deficiency at <3 mo of age between May 2001 and May 2003 were reviewed. A total of 42 infants (27 boys and 15 girls) were diagnosed with vitamin D deficiency in the first 3 mo of life during this 2-y period. The age of infants at diagnosis was 60 +/- 19 d (range 32-112 d). The majority (78.7%) presented with seizures. No skeletal deformities were detected clinically, and radiological findings were subtle. All infants had low serum calcium levels but serum phosphorous levels varied. Eight infants (19.0%) had low, 19 (45.3%) had normal, and 15 (35.7%) had elevated serum phosphorous levels. Serum 25-hydroxyvitamin D levels in those measured (29 infants and 15 mothers) were <37.5 nmol/L. Most infants (83%) were exclusively breast-fed without supplemental vitamin D, and none of the mothers were supplemented with vitamin D during pregnancy. All mothers had limited sunlight exposure and 33 of 42 mothers (78.6%) wore concealing clothing. The majority of young infants diagnosed with vitamin D deficiency present with seizures, have low dietary vitamin D intake, and mothers with poor vitamin D reserves. Evaluation of vitamin D status should be included into the workup of hypocalcemia in early infancy. Prevention of deficiency by supplementing pregnant women and infants who are exclusively breast-fed is essential.