It is well established today that an optimal vitamin D intake plays a crucial role in the constitution of optimal osseous mass during childhood, and hence in the prevention of the osteoporosis in adults. The prevalence of the vitamin D deficiency is increasing globally and Algeria is no exception in this regard. Our study is the first to be carried out with healthy children of preschool age in North Africa. OBJECTIVE The study aimed to evaluate the vitamin D status of a pediatric population, during all four seasons of the year, living in the north of Algeria, as well as to estimate the prevalence of vitamin D deficiency, identifying the potential risk factors. METHODS This was an analytic and cross-sectional study carried out between March 2014 and March 2016 with healthy preschool infants from an urban environment in the town of Hussein Dey. A total of 1016 infants aged 9-72 months were included during this period. The consensual threshold value was 20ng/mL. RESULTS The sex ratio was of 1.47 (535 boys/481 girls) and the average age of the children was 36.5±1.79 months. The daily average calcium ratio was 395±23 mg/with food contributions in vitamin D at an estimated average of 164 UI/day (4.1μg/day). The average concentration of the total 25-OHD for all four seasons of the year was 18.6±10.4ng/mL with an average rate of parathyroid hormone (PTH) of 30.9±14.6pg/mL. There was a highly significant inverse correlation between the serum level of vitamin D and PTH (r=-0.57; P=0.0001), the point of inflection was situated at 34.1ng/mL. The prevalence of vitamin D deficiency follows a seasonal variation that is statistically significant (P=0.0001), and the prevalence is higher during the autumn-winter period. The risk factors identified by multiple logistic regression were autumn-winter season (OR: 7; 95% CI: 3-11; P=0.001), age less than 24 months (OR: 3.8; 95% CI: 3.4-4.4; P=0.0001), high body mass index (OR: 2; 95% CI: 1.2-3.2; P=0.3), darker skin pigmentation (OR: 2.8; 95% CI: 2.2-5.2; P=0.001), duration of sunlight exposure less than 15min (OR: 6.1; 95% CI: 3.6-10.2; P=0.0001), low socioeconomic status (OR: 3.9; 95% CI: 1.5-4.3; P=0.01), calcium intake lower than 500 mg/day (OR: 2.5; 95% CI: 1.8-6; P=0.001), and a weekly dietary intake of vitamin D lower than 200 UI (OR: 2.6; 95% CI: 1.6-4.2; P=0.02). CONCLUSIONS No studies have been conducted in north Africa or Algeria concerning healthy preschool children; however, this population has a rapid growth rate and deserves special attention. The prevalence of vitamin D deficiency in the children of this study was higher than that reported in studies of children of the same age living in Europe or America, despite the fact that Algeria is closer to the equator (36° latitude north). CONCLUSIONS The changes experienced by Algerian society and the shorter exposure of the population to the sun call for more efforts regarding the detection and treatment of vitamin D deficiency, as well as an update of the vitamin D supplementation schedule.