In 1979 Pearson described a syndrome, in which the main symptoms were severe sideroblastic anemia and exocrine pancreas dysfunction. The aetiology was still unknown. A decade later, the Pearson syndrome can be described as a lethal multisystem disorder, in which the bone marrow and exocrine pancreas show major dysfunction, but also other organs (like kidneys, liver, gut and skin) can be affected. These patients also show growth retardation. The study of the mitochondrial DNA allowed identification of a deletion in the mitochondrial DNA. The case of a patient suffering from Pearson's syndrome is reported.