The alpha thalassaemia diseases in most cases are caused by deletions that affect one or two of the alpha genes, being less frequent the cases due to punctual mutations, insertions or deletions of a few pairs of bases, which have been denominated no deletion a thalassaemias. The objective of this investigation was to determine the incidence of the no deletion alpha thalassaemia in patients with a thalassaemia using molecular biology techniques. We studied 517 individuals of the San Carlos Hospital (Thalassemia Molecular Research Center, Madrid-Spain) between January 2001 and December 2003, in whom iron deficiency anemia had been ruled out, that presented microcytosis and hypochromia and that presented normal HbA2, HbF and EEF from normal Hbs. The two types of no deletion a thalassaemia most frequently described in the Mediterranean were studied: 1) alpha Hph due to deletion of 5bp in the IVS I and 2) alphaNco due to a change in the initiation codon of the gene. Of the 517 cases studied, 40 (7.7% of the cases) represented a no deletion alpha thalassaemia. Of these cases, 28 were positive for alphaHph of the alpha2 gene, 24 in the heterozygote state, one homozygote and three double heterozygotes associated with the 3,7 kb deletion. The remaining 12 cases were positive for the alphaNco of the alpha2 gene, 10 heterozygotes, one homozygote and one double heterozygote associated with the 4,2 kb deletion. The no deletion alpha thalassaemias represent < 8% from the cases in our environment. The alphaHph is the most frequent type of no deletion a thalassaemia and its haematological abnormalities are more manifest that the ones present in the cases of alphaNco.