Severe acquired aplastic anaemia (SAA) is a life-threatening disease characterized by pancytopenia and hypoplastic bone marrow. Autologous T lymphocytes are thought to cause bone marrow failure by immune-mediated excessive apoptosis of stem and progenitor cells. The disease is subclassified into a severe (neutrophil count, > 0.2 x 10(9)/L [> 200/microL]) and a very severe (< 0.2 x 10(9)/L [< 200/microL]) (vSAA) form. We report the results of a prospective multicenter trial with a combined immunosuppressive regimen of cyclosporin A (CSA), anti-thymocyte globulin (ATG) and, in cases with neutrophil counts fewer than 0.5 x 10(9)/L (< 500/microL), granulocyte colony-stimulating factor (G-CSF) for treatment of SAA in children. Children with vSAA showed a higher rate of complete response than did children with SAA (68% versus 45%; P = .009), as well as better survival (93% versus 81%; P < .001). Thus, in children with SAA a more severe disease stage at diagnosis indicates a favorable outcome with immunosuppressive therapy.