Background: Ischemia-modified albumin (IMA) is an altered type of serum albumin that forms under conditions of oxidative stress and an independent predictor of major adverse cardiovascular events. Objectives: To measure the levels of IMA in 45 children and adolescents with β-thalassemia major (β-TM) compared with 30 healthy controls and assess its relation to lipid peroxidation, vascular complications and subclinical atherosclerosis. Methods: β-TM patients without symptoms of heart disease were studied focusing on transfusion history, chelation therapy, serum ferritin, malondialdehyde (MDA) and IMA levels. Echocardiography was performed and carotid intima media thickness (CIMT) was assessed. Results: IMA and MDA levels were significantly higher in β-TM patients compared with controls (p < 0.001). IMA was higher among patients with heart disease, pulmonary hypertension risk and serum ferritin ≥2500 µg/l than those without. TM patients compliant to chelation had significantly lower IMA levels. IMA levels were positively correlated to MDA and CIMT while negatively correlated to ejection fraction and fractional shortening. Conclusion: Our results highlight the role of oxidative stress in the pathophysiology of vascular complications in thalassemia. IMA could be useful for screening of β-TM patients at risk of cardiopulmonary complications and atherosclerosis because its alteration occurs in early subclinical disease.