Most of the biological actions of vitamin D are mediated by an intracellular receptor (VDR) in which several single nucleotide gene polymorphisms have been identified. Vitamin D deficiency is increasingly identified among thalassemic patients and recent evidence links it with myocardial iron accumulation. The aim of this work was to assess the distribution of the Fok-I polymorphism of the VDR gene among Greek children and young adults with beta-thalassemia major and to investigate its association with 25(OH)D(3) and 1,25(OH)(2)D(3) serum levels. Sixty-nine thalassemic patients (35 females and 34 males), with a mean age of 23·05±6·07 years, participated in the study. Genotype frequencies of Fok-I were similar to those previously reported for other populations; 44·9% of the patients were homozygotes for F allele, 43·5% were heterozygotes and 11·6% were homozygotes for the f allele. Low levels of serum 25(OH)D(3) were recorded, as 41 patients (59·4%) were below the cut-off limit of 50 nmol/l that determines deficiency, whereas, levels of 1,25(OH)(2)D(3) showed wide variability ranging from deficiency (≤50 pmol/l) in 34 patients (49·3%) to excess (≥125 pmol/l) in 13 patients (18·8%). When stratifying patients according to serum 1,25(OH)(2) D(3) concentrations, a higher prevalence of the f allele was observed in the deficiency group (P = 0·03). A comparison of the serum concentrations of the two vitamin D metabolites produced a trend towards a negative correlation (r = -0·204, P = 0·09). Further studies are required to assess the genetic contribution to the regulation of vitamin D metabolites in the serum of patients with beta-thalassemia major.