This report describes a follow-up study in which the prevalence of emotional and behavioral problems in a group of 42 children and adolescents treated for leukemia is compared with the prevalence of problems in a matched control group selected from the general population. The prevalence of problems among the siblings of the two groups, and the adjustment of the two groups of families, are also examined. The Achenbach Child Behavior Checklist, for completion by parents, and the Achenbach Child Behavior Checklist and Rutter B2 Behavioural Scale, for completion by teachers, are used to identify both social competence and behavioral problems. In addition, the Family Concept Inventory is used to evaluate the adjustment of families. The leukemic children and adolescents were found to have significantly more problems and less social competence, particularly in school-related activities, than either the control group or their own siblings. There was no difference in the prevalence of problems between the two groups of siblings, nor between the two groups of families. It is suggested that careful prospective studies are needed to identify the cause of the problems experienced by the leukemic children and adolescents so that programs may be developed to prevent their emergence.