Background: Delayed umbilical cord clamping could increase iron stores and prevent iron deficiency in infants. To test this hypothesis we measured serum ferritin and hemoglobin levels at six months of age in term infants who had participated in a randomized controlled trial, assessing the effect of cord clamping timing on neonatal hematocrit values and clinical outcome. Main outcome measure. Serum ferritin level at six months of age. Methods: Out of the 276 mothers and their infants that participated in the initial study, 255 (92.4%) were followed up to six months and included in this study. Of these, 86 had their cords clamped within the first 15 seconds (early clamping), 83 at one minute, and 83 at three minutes. The pediatricians in charge of the evaluations during the follow-up period and personnel in charge of the biochemical tests were blinded to the assignment group. In all but 3 infants the ferritin levels and hemoglobin levels were measured at six months of age. Results: Mothers and infants in the three groups had similar baseline characteristics. Serum ferritin levels were significantly higher in the infants of the three minutes group than in the infants of the early group: 33.2 μg/L vs. 20.9 μg/L (geometric mean ratio: 1.6; 95% CI: 1.2 to 2.11) but no difference was observed in one minute group (25.5 μg/L) vs. early group. There were no significant differences in mean hemoglobin values, 10.6 g/dl (SD1,1); 10.8 g/dl (SD 0.9) and 10.7 g/dl (SD 1.0) between groups early, one minute, and three minutes, respectively. Although there were no significant differences between groups, the prevalence of iron deficiency anemia (hemoglobin < 10.5 g/dl and ferritin < 9 μg/L) was 3 times more frequent in early clampling group (7.2%) than in three minutes group (2.4%) (RR: 0.30; IC 95%: 0.10-1.60). Conclusions. Delayed umbilical cord clamping at three minutes significantly increases serum ferritin levels in infants at 6 months of age. No significant differences were found between groups in mean hemoglobin levels.