Abstract 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/l), insufficient (25–50 nmol/l), sufficient (50–75 nmol/l) and optimal (≥75 nmol/l). 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/l (mean 47·2 ( sd 14·6) nmol/l); 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.