beta-Thalassaemia is manifested by severe anaemia and extensive bone pathology. Similar pathology may also result from other forms of anaemia. To clarify the precise cause, we performed DNA analyses on archaeological remains of a child with severe bone pathology. We found homozygosity for frameshift in codon 8 of beta-globin, causing a beta-null phenotype. Paradoxically, the child died when eight years old, whereas such patients are transfusion dependent from early infancy. An infrequent polymorphic marker in the child's DNA, and information from present-day patients, indicated that amelioration of the clinical condition was due to elevated fetal haemoglobin production. Thus this analysis provided not only precise diagnosis of a genetic disease but also allowed clarification of the molecular mechanism underlying the clinical presentation.