Various recent publications reported clinical manifestations of vitamin D deficiency in infants. Furthermore new research revealed additional properties of vitamin D for bone health and in the prevention of chronic diseases. However, prevalence data on actual supplementation rates are scarce. This study reports the prevalence of vitamin D supplementation in infants in Switzerland and presents risk factors for non-supplementation.; In 2003, mothers of 2861 randomly selected infants aged 0-9 months received a questionnaire on infant feeding, including a question on vitamin D supplementation. The prevalence of vitamin D supplementation was calculated and its dependency on various factors analysed by multiple logistic regression.; 64% of the infants had received vitamin D. The regression analysis yielded various significant risk factors for non-supplementation: young maternal age, German language region, Swiss nationality, siblings and breastfeeding. Protective factors were intake of folic acid during pregnancy and professional information on infant feeding. The protective effect of professional information varied significantly by region.; Given that the supplementation of vitamin D is recommended for all infants, the supplementation prevalence in Swiss infants is unsatisfactorily low. Various risk factors were identified and a positive impact of professional counselling on the supplementation rate could be demonstrated. In view of the new evidence emerging on additional preventive properties of vitamin D and the resurgence of rickets, the importance of vitamin D for infant health and ways to improve its promotion must be discussed anew.