Four hundred and four children with Hodgkin's disease (stage I-IV) were treated in seven cooperating centers of Polish Paediatric Leukaemia/Lymphoma Study Group between 1988 and 1996. Mediastinal masses and/or hilar involvement were found in 261 (65%) patients. Remission was obtained in 256 (98%) of this group. In 31 (12%) children residual mediastinal/hilar masses were found after completing the treatment. For this reason in 13 cases the number of chemotherapy courses and/or the dose of radiation therapy were increased. In two cases thoracotomy or thoracoscopy were performed, and in one case gallium scan was performed. In none of these patients active disease was found. Relapses occurred in 4 (12.9%) from the group of 31 children with residual mediastinal/hilar involvement 8-15 months after cessation of the therapy. Twenty seven children have been in first remission for 5-113 months (median, 34). In 225 patients with a complete resolution of their mediastinal/hilar masses, relapses occurred in 13 (5.7%) cases. Patients with residual mediastinal mass should be carefully evaluated before making a decision to complete their treatment, including CT scan, MRI, and gallium scan. In doubtful cases histopathological verification should be done.