Thalassemia is a group of hereditary hemolytic anemias, caused by a quantitative violation of the globin chains synthesis. In adults, the main hemoglobin (HbA) consists of two a- and two b-chains. Normally, regulatory mechanisms maintain a balance between a- and non-a-globin chains in a 1:1 ratio. Mutations in the b-globin gene, leading to a quantitative disruption of the synthesis of b-globin chains, lead to the development of b-thalassemia. In such patients, the presence of concomitant breakdowns of a-globin genes can determine the variability of the clinical symptoms, both mitigating or increasing the severity of the manifestations of beta-thalassemia. The article describes two clinical cases of transfusion-dependent thalassemia with a rare genotype: aaa^anti-3.7/aa and b-thalassemia. Parents gave their consent to use information about the child, including fotos, in the article.