Three male patients with X-linked alpha-thalassemia/mental retardation (ATR-X) syndrome in a large French family are reported. Diagnosis was suspected on particular craniofacial dysmorphism associated with severe mental retardation and X-linked transmission. Hematological investigations, and in particular presence of Hb H inclusions in two of the boys, confirmed diagnosis. The clinical, hematological and radiological features are discussed in order to better define what appears to be a characteristic phenotype.