Although routine Fe supplementation in pregnancy is a common practice, its clinical benefits or risks are uncertain. Children born to mothers in the Fe group in a trial of Fe supplementation in pregnancy have been found to have a significantly higher risk of abnormal behaviour at 4 years of age than those born to mothers in the placebo group. The objective of the present study therefore was to determine whether Fe supplementation in pregnancy influences child behaviour at early school age. The study was a follow-up of children at 6-8 years of age after women (n 430) were randomly allocated to receive a daily Fe supplement (20 mg) or placebo from 20 weeks gestation until delivery. The supplement reduced the incidence of Fe-deficiency anaemia at delivery from 9 % to 1 %. Child behaviour and temperament were assessed using the Strengths and Difficulties Questionnaire and the Short Temperament Scale for Children. Of the children, 264 (61 %) participated in the follow-up. Mean behaviour and temperament scores and the proportion of parent-rated and teacher-rated abnormal total difficulties scores did not differ between the Fe and placebo groups. However, the incidence of children with an abnormal teacher-rated peer problems subscale score was higher in the Fe group (eleven of 112 subjects; 8 %) than in the placebo group (three of 113 subjects; 2 %); the relative risk was 3.70 (95 % CI 1.06, 12.91; P = 0.026). We conclude that prenatal Fe supplementation had no consistent effect on child behaviour at early school age in this study population. Further investigation regarding the long-term effects of this common practice is warranted.