Studies of renal involvement in thalassemia syndromes have been varied and few. The most important cause of mortality and morbidity in these patients is organ failure due to iron deposition. We report here a cross-sectional study carried out between February 2005 and February 2006 on all beta-thalassemia major patients being treated in Mofid Children's hospital, Tehran. The aim of the study was to detect renal dysfunction in these patients. The patient cohort consisted of 103 patients with various disease severities. Fresh first morning urine samples were collected and analyzed for sodium (Na), potassium (K), calcium (Ca), creatinine (Cr), phosphate, uric acid (UA), N-acetyl beta-D-glucosaminidase (NAG) and amino acids. We also carried out a complete blood count evaluation and assayed fasting blood sugar and serum ferritin, sodium, potassium, creatinine, uric acid and amino acids in all patients. The mean age of our patient cohort was 12.5 ± 5.53 years and 53.4% were female. Abnormal levels of urinary NAG were detected in 35.9% of patients (confidence interval 26-45%). Abnormal levels of fractional excretion (FE)-Na, FE-K and FE-UA and abnormal urine protein Pr/Cr and urine Ca/Cr ratios were present in 29.1, 7.8, 52.4, 0.3 and 22.3% of the patients, respectively. There was a significant relationship between urinary NAG and the age of the patient (R = 0.35), duration of deferoxamine therapy (R = 0.31), duration of receiving blood transfusions (R = 0.34) and level of fasting blood sugar (R = 0.2). We concluded that renal disorders are not rare in patients with beta-thalassemia major and that they may increase in terms of frequency with age, increased duration of transfusion and deferoxamine usage and high levels of blood sugar.