Iron deficiency in children has been associated with behavioural disorder and developmental delay. Screening for iron deficiency was offered to all 527 children aged between one and four years in an inner city practice. Half the children belong to an ethnic minority group, and there is widespread social deprivation in the area. Capillary haemoglobin concentration and mean corpuscular volume were estimated in 365 children (69%). Dietary history, birth weight and current weight were also recorded. Fifty-eight (16%) of the children were iron deficient as defined by a mean corpuscular volume of less than 75 fl and/or a haemoglobin concentration of less than 10.5 g dl(-1). All were hypochromic and among 23 tested all had serum ferritin levels below 10microg I(-1). Twenty-one children (5.8%) were anaemic (haemoglobin concentration less than 10.5 g dl(-1)). Anaemia was significantly more common among children who were currently underweight but was not related to weight at birth. Iron deficiency was significantly more prevalent in non-Caucasian children - 25.0% compared with 7.8% of Caucasian children. There was also a significant linear decrease in iron deficiency with increasing age. Sex, weight at birth, current weight, whether breast fed, age weaned or whether on a vegetarian diet were not significant factors in iron deficiency. Iron supplements were given to all the children with iron deficiency.In view of the high prevalence of iron deficiency, all children in the practice are now routinely offered screening for iron deficiency at the age of 14 months. The programme has been welcomed by all parents. It is suggested that screening for iron deficiency should be part of routine child surveillance.