To evaluate the prognosis of breath holding spells (BHS) after iron treatment, 91 children (56 boys, 35 girls) aged between 6 months and 40 months (median, 17) were followed prospectively for a median of 45 months (range, 6-89). In 49 of the children, the frequency of BHS was less than 10 each month, in 22 it was 10-30 each month, and in 20 more than 30 each month. The spells were cyanotic in 60 children. All patients were evaluated initially and during follow up for haematological indices. Electroencephalographic and electrocardiographic abnormalities were also recorded. Sixty three patients were found to have iron deficiency anaemia and were treated with iron (6 mg/kg/day) for three months. Other patients were not given any treatment. After three months, there was a significant difference for correction of cyanotic spells between children who had been treated with iron and those who had not (84.1% v 21.4%). During further follow up, febrile convulsions occurred in 10 children (six were on iron treatment initially). It appears that treating iron deficiency anaemia is effective in reducing the frequency of BHS.