Introduction: Nowadays, a significant number of children with acute leukemia can be cured. Iron overload, related to blood transfusions and its long-term complications, remains a problem. Elevated ferritin concentration is often observed in this group. The aim of this study was to evaluate the prognostic value of serum ferritin on long-term outcomes in children treated for acute leukemia. Material: We studied 71 patients treated for acute lymphoblastic (ALL) or myeloblastic (AML) leukemia between 2005 and 2011. Serum ferritin concentration, serum transaminases activity, lactic dehydrogenase and C-reactive protein levels (CRP) were analysed. Serum ferritin >1,000 µg/L was considered to be a marker of iron overload. Results: Thirty-seven patients (52.1%) had iron overload. Ferritin serum concentration correlated with alanine aminotranferase activity (p =0.001) and CRP concentration (p =0.012). A total of 19 (26.76%) patients died during follow-up. Ferritin level was higher in patients with AML vs. ALL. There was a significant difference in long-term outcomes with respect to high ferritin concentrations, both in patients undergoing haematopoietic cell transplantation (HCT) and in the non-HCT group. Conclusions: In both groups, patients with higher ferritin concentrations had worse overall and event-free survivals and a higher relapse incidence. Ferritin concentration >1,000 µg/L was the strongest determinant of long-term treatment outcome. Ferritin serum concentration >1,000 µg/L is an adverse prognostic marker of survival in children with acute leukemia treated with chemotherapy with or without HCT.