Abstract Background Increasing numbers of children are presenting with nutritional rickets. Rickets affects mainly dark-skinned infants being breastfed for prolonged periods without vitamin supplementation. The main aim of this study was to assess health visitors’ (HV) knowledge of the government guidelines for vitamin supplementation for infants and children and the advice given to mothers. Methods Questionnaires were sent to all HV in Brent, Harrow and Westminster Primary Care Trusts (PCT). Information received was collated and used to assess HV knowledge. Results A total of 98 (69%) questionnaires were returned from HV. Seventy-nine HV (81%) recommend vitamins for the breastfed infant at 6 months or younger, 18 of which would recommend at 1 month of age. Fifty-six HV (57%) recommend vitamins until 5 years of age. Seventy-nine HV correctly identified Asians to be at risk of developing rickets. However, only 28 and 16 HV, respectively, identified Black Africans and Black Caribbeans to be at risk. Conclusion Rickets has become a national public health issue. The majority of HVs is advising vitamin supplements according to government guidelines for breastfeeding infants and the age to which children should continue vitamin supplements. However, ethnic minority groups are at increased risk of vitamin D deficiency. Consequently, greater awareness needs to be raised about the government guidelines for vitamin D supplementation for ethnic minorities to ensure all HVs are imparting consistent, correct advice to these families.