Most patients homozygous for beta thalassaemia have beta thalassaemia major, a severe illness requiring regular blood transfusions. However, some homozygotes remain well without regular transfusions and are described by the term thalassaemia intermedia. Three factors have now been identified which may result in beta thalassaemia intermedia: the inheritance of mild beta+ thalassaemia mutations, the co-inheritance of alpha thalassaemia and the inheritance of factors enhancing gamma-globin gene expression. In addition other less common genetic interactions also result in thalassaemia intermedia such as the compound heterozygous state for beta and delta beta thalassaemia. These patients need careful clinical follow up, especially since the complications of hypersplenism and iron overload (even in the absence of blood transfusion) can occur.