Reduction of bone density and its associated morbidity is recognized in young adults with beta-thalassaemia major, but the aetiology is not clear. This study used dual X-ray absorptiometry (DXA) to look at bone mineral apparent density (BMAD) in children and young adults with thalassaemia in a predominantly Asian population, in the context of sexual maturation. Fifty-five patients were scanned (mean age 13.8 years, range 5.9-37.5) and BMAD z-scores were calculated using normal data from locally recruited control subjects. Eighteen patients had undergone bone marrow transplantation (BMT) and the remainder were on a transfusion/chelation regimen. BMAD z-scores ranged from -3.3-1.6 with a mean of -0.92. No difference in BMAD was found between those patients treated conventionally and those who had undergone BMT. When comparing mean BMAD z-score according to sexual maturation, there was a highly significant difference (P < 0.0001) between those whose pubertal maturation was age appropriate (mean z-score -0.22), when compared with those who had disordered puberty (mean z-score -1.82). We have shown that failure to progress normally through puberty is highly significant in the failure of adequate bone mineralization and achievement of peak bone mass in thalassaemic patients. The management of these patients should therefore be pro-active to anticipate problems and facilitate normal sexual maturation.