In order to investigate the current health and nutrition status of mothers and children in Mongolia, a regionally stratified survey of 977 randomly sampled households was conducted during July and August 1997. The prevalence of children aged 6-60 months who demonstrated one or more of three main clinical signs (i.e. rachitic rosary, Harrison's groove and delayed closure of fontanelle) was found to be 69.8%. Although a nationwide supplementation programme exists, caretakers reported only 66.2% of children under 3 years of age had received at least one vitamin D supplement in the 6 months preceding the survey. The lack of adequate UV-B rays during the winter months (i.e. October-April) and traditional swaddling of infants for a minimum of 3 months and a maximum of 9-12 months are likely to contribute to the prevalence of rickets in Mongolia. The high prevalence of rickets in Mongolian children is a serious public health concern. In addition to the adverse effects on growth, development and immune function, it is probably indicative of widespread subclinical vitamin D deficiency.