Our objective was to assess the utility of PET-CT in five pediatric patients with Langerhans cell histiocytosis (LCH) who underwent PET-CT imaging for clinical staging and determination of lesion activity at various stages of treatment and follow-up. PET-CT combines the anatomic detail of CT and the physiologic activity of (18)F-FDG imaging. We conclude that PET-CT information is clinically useful to evaluate disease activity and response to therapy and provides information that cannot be obtained from technetium 99m methylene diphosphonate bone scans or radiographs.