Thirty-four children with aplastic anaemia who presented between 1964 and 1984 are reviewed. Their ages ranged from one to 13 years (median, seven years). Twelve children had constitutional aplasia; nine of 11 children had responded to androgen and corticosteroid therapy. However, by actuarial analysis, only 48% would survive at five years and only 16% after 10 years. Twenty-two children had acquired aplasia; in 16 children this had no obvious cause. By means of the criteria of the International Aplastic Anemia Study Group, patients were categorized into severe and non-severe groups at diagnosis. Severe disease was present at diagnosis in nine of 22 children with acquired aplasia but in no child with constitutional disease. Two patients with severe acquired aplasia showed a transient response to androgen or corticosteroid therapy, whereas five of nine children with acquired aplasia which was not severe showed a sustained response to such therapy. A significant difference in survival times was seen between severe and non-severe groups at five years; two (17%) of nine children with severe aplasia survived, compared with eight (67%) of 12 children with non-severe aplasia. Three children with severe aplasia who were treated with antilymphocyte globulin showed no improvement. Of five children who underwent bone-marrow transplantation for severe or progressive disease, four survived. It is concluded that bone-marrow transplantation, as a matter of urgency, is the treatment of choice for severe acquired aplastic anaemia; it is also recommended for mild acquired or constitutional aplasia when progressive disease is present or where transfusion therapy will be required. Antilymphocyte globulin is an alternative form of treatment for acquired disease. Androgen therapy is effective in the treatment of non-severe acquired and constitutional aplastic anaemia.