Aim: To establish the frequency and causes of vitamin D insufficiency in healthy female adolescents in Izmir, Turkey. Methods: 64 adolescents from alow-(Ikinci Inonu) and a high- (Ilica) socio-economic settlement were included. Parents' monthly income was classified as low, middle and high. The blood samples were drawn at the end of the summer and winter periods. Results: Vitamin D insufficiency percentages for the end-of-winter period were 59.4% in Ikinci Inonu and 15.6% in Ilica, and for the end of summer 25% and 15.6%, respectively. Calcidiol levels of cases from Ikinci Inonu were found to be lower compared with the levels of cases from Ilica (349/15 vs 599/24 nmol/l for end of winter, p = 0.000; 519/22 vs 659/28 nmol/l for end of summer, p = 0.03). Calcidiol levels of cases whose parental monthly income was low and whose mothers were illiterate were significantly lower than the others (489/18 vs 659/29 nmol/l for end of summer, p = 0.01; 339/16 vs 56 +/- 23 nmol/l for end of winter, p = 0.000; 45 +/- 13 vs 64 +/- 29 nmol/l for end of summer, p = 0.007; 36 +/- 17 vs 51 +/- 25 nmol/l for end of winter, p = 0.02; respectively).