Objective: To describe the vitamin D status of Belgian children and examine the influence of non-nutritional determinants, in particular of anthropometric variables. Design: Cross-sectional data of Belgian participants of the EU 6th Framework Programme IDEFICS (Identification and Prevention of Dietary- and Lifestyle-Induced Health Effects in Children and Infants) Study. Setting: 25-Hydroxyvitamin D (25(OH)D) was measured using RIA. Vitamin D status was categorized as deficient (<25 nmol/1), insufficient (25-50 nmol/1), sufficient (50-75 nmol/1) and optimal (>= 75 nmol/1). Anthropometric measurements included height, weight, waist and hip circumferences and triceps and subscapular skinfold thicknesses. Subjects: Children (n 357) aged 4-11 years. Results: Serum 25(OH)D) ranged from 13.6 to 123.5 nmol/1 (mean 47.2 (SD 14.6) nmol/1); with 5% deficient, 53% insufficient, 40% sufficient and 2% optimal. No significant differences were found by age and gender. Significant differences in 25(OH)D were observed for month of sampling (P < 0.001), number of hours playing outside per week (r = 0.140), weight (r = -0.121), triceps (r = -0.112) and subscapular (r = -0.119) skinfold thickness, sum of two skinfold thicknesses (r = -0.125) and waist circumference (r = -0.108). Linear regression analysis of 25(OH)D adjusted for age, month of sampling and hours playing outside per week suggested that (i) weight, (ii) BMI Z-score, (iii) waist circumference and (iv) triceps and subscapular skinfold thickness (as well as the sum of both) independently influenced 25(OH)D. Conclusions: The majority of Belgian children had a suboptimal vitamin D status, with more than half having an insufficient status in winter and spring. Month of the year, weekly number of hours playing outside and body composition - both central and abdominal obesity - were identified as important determinants of vitamin D status in Belgian children.