The child with haemoglobin H (HbH) disease and multiple congenital abnormalities reported by Borochowitz et al (1970) has been more fully investigated in view of the recent report by Weatherall et al (1981) of a 'new' syndrome of HbH disease and mental retardation. Restriction enzyme analysis indicates that the child's HbH disease results from the inheritance of an alpha-thalassaemia 2 chromosome (-alpha/) from his mother and, from his father, a chromosome which has undergone a deletion including the zeta- and alpha-globin genes as well as an undefined length of DNA. Striking similarities between our patient and Weatherall et al's patients at the clinical level and between our patient and their patient number 1 at the molecular level, confirm that a new syndrome has been defined.