The toddler diet in the U.K. changed considerably during the 25 years between the last two national dietary surveys, and these and other reports suggest that the nutritional intake of many toddlers does not comply with national recommendations. This is a concern for parents and health care workers because both deficiencies and excesses in nutrition are associated with increased risk of diseases, such as iron deficiency anaemia, rickets, dental caries and diseases related to obesity. Paradoxically, a decrease in energy intake has been accompanied by a rise in obesity, while a parallel fall in vitamin and mineral intake has been seen in tandem with an increase in diseases associated with nutritional deficiency. Establishing good dietary habi in early childhood is therefore important for short-term health. Dietary patterns at this time may be crucial to later behaviour and, if carried through to adulthood, may affect long-term health. In particular, deficiencies of micronutrients such as iron, zinc and vitamin D are a cause for con cern. Childhood diseases such as rickets, which affects bone development and was thought to have been eradicated, have re-emerged in recent years and the prevalence of iron deficiency anaemia has increased, particularly among migrant populations among migrant populations. Part 1 of this review considers the relationship between current toddler diet and micronutrient deficiencies, focusing on the impact of deficiency on both short- and longterm health. In Part 2 (to be published in Journal of Family Health Care 2007; 17[6]), the authors will consider effects on health of nutritional imbalance resulting from overconsumption of energy and nutrients.