A total of 304 children under the age of 15 years with acquired severe aplastic anemia (SAA) received immunosuppressive therapy (IS) (n = 133) or a matched bone marrow transplant (BMT) (n = 171). The projected 10-year survival is 48% and 63% respectively (p = 0.002). Results following BMT have improved considerably over the years from 49% in 1970-80, to 70% in 1981-83 (p = 0.002) and to 81% between 1984-88 (p = 0.08). Other favorable prognostic factors are the use of cyclosporin A (p = 0.004), no previous therapy (p = 0.006) and early BMT (p = 0.009). In multivariate analysis only the year of treatment proved significant (p = 0.02). In contrast, results of IS are greatly dependent on the severity of pre-treatment neutropenia with survival of 56% versus 37% for neutrophils more or less than 0.2 x 10(9)/l (p = 0.003). Poor survival was associated in univariate analysis with female sex (43%), post-hepatitis SAA (37%), children not receiving androgens (38%) and patients younger than 5 years (35%), especially if associated with a low neutrophil count (11%). In multivariate analysis only the degree of neutropenia proved significant (p = 0.005). These results suggest that IS is a satisfactory alternative therapy for children with moderately SAA in the absence of an HLA-identical sibling, although BMT remains the treatment of choice. In children under 5 years with very SAA, results with IS are so poor that a search for an unrelated matched donor is justified as early as possible.