The incidence of aseptic necrosis of femoral head in homozygous beta-thalassaemia (Cooley's anaemia)--which is indeed significantly high--is not satisfactorily referred in late literature regarding haemolytic syndromes. Therefore, 4 cases of osteonecrosis of femoral head, recently recognized in a series of 280 patients affected by Cooley's anaemia (14.5 0/00) are presented, and a review of hypotheses about the pathogenesis of the lesions is considered. In Cooley's anaemia, the skeletal lesion (osteoporosis) must be believed as a propitious state, in which some other pathogenetic events (i.e. local ischemia, bony age, etc.) and microtraumas overlap. In any case, characteristic blood circulation of the femoral head is the "conditio sine qua non" in developing osteonecrosis.