Introduction - The objective was to describe the prevalence of vitamin D deficiency and its associated factors in the adult population living in metropolitan France. Methods - The National Nutrition and Health Survey (ENNS), conducted in 2006–2007, included the collection of sociodemographic and dietary data, anthropometric measurements (weight, height), and a blood sample. Serum 25-hydroxyvitamin D (25(OH)D) levels were measured. Factors associated with the risk of "moderate to severe" (<20 ng/ml) or "severe" (<10 ng/ml) deficiency were identified using multivariate logistic regression. Results - The analyses included 1,587 adults not taking vitamin D-based medication. The mean 25(OH)D concentration was 23.0 ng/ml [22.3–23.6]; 80.1% [77.0–82.8] of adults had insufficiency (<30 ng/ml), 42.5% [39.1–45.9] had moderate to severe deficiency, and 4.8% [3.6–6.3] had severe deficiency. The risk of moderate to severe deficiency was associated with being born outside Europe (ORa=2.1, p<0.02), not going on vacation (ORa=1.7, p<0.01), having a low level of physical activity (ORa=1.9, p<0.01), being sedentary (ORa=1.6, p<0.01), and living in an area with low sunlight exposure (ORa=2.7, p<0.01). The risk of severe deficiency was associated with being born outside Europe (ORa=10.7, p<10⁻³), living alone (ORa=2.8, p<10⁻³), and not going on vacation (ORa=4.6, p<10⁻³), but was independent of physical activity level and sedentary behavior. Conclusion - In France, severe vitamin D deficiency is rare and affects vulnerable populations (low socioeconomic status and reduced sun exposure). Moderate deficiency, however, is common. Modifying certain lifestyle habits, particularly increasing physical activity, should help reduce its prevalence. (R.A.)