We have identified the case of a 9-months-old girl with heterozygotic thalassemia and triplication of alpha genes of globin (alpha alpha alpha 3.7). Molecular defect of thalassemia was a mutation without sense of 39 codon. Patient's phenotype was an intermediate thalassemia with moderate splenomegaly and marked unbalance on the globin chains. This is the first case of intermediate thalassemia, through this mechanism, described in Spain.