Aim: The aim of this research is to study the variance of erythrocyte ferritin (EF) in patients with chronic renal failure (CRF) and heterozygous β-thalassemia (β-TA), as well as the use of EF as a more reliable index for assessing the body iron status. Methods: We studied 63 subjects with CRF, 40 subjects with heterozygous β-TA, 53 subjects with CRF and heterozygous β-TA and 24 normal subjects. In 11 patients with CRF and heterozygous β-TA, sternal bone marrow aspiration was performed to evaluate iron stores in the bone marrow. EF was determined in the hemolysate of washed erythrocytes by a radioimmunoassay. Results: EF showed the strongest correlation with bone marrow iron (p < 0.001) in comparison with the remaining hematological parameters that were examined. Patients with CRF without heterozygous β-TA showed an increase in serum ferritin (SF), even in cases of iron deficiency. In the group of heterozygous β-TA without renal failure, 22.5% of patients showed an increased EF content up to 150 ag/cell and a tendency for iron overload. Patients with CRF and heterozygous β-TA showed a high value of EF, up to 200 ag/cell, and iron overload in 22.6%, almost the same proportion as in the previous group. It was also observed that a high value of SF does not indicate iron overload for these patients. In the group of hemodialysis, patients without heterozygous β-TA who were under erythropoietin (EPO) treatment presented iron deficiency. Many patients with CRF and heterozygous β-TA who were taking EPO presented iron overload, while very few of them presented iron deficiency. Conclusion: These findings suggest that EF is a reliable index for assessing the iron status in patients with CRF and heterozygous β-TA.