In the last decade, FDG-PET scans have had a major impact on the treatment of patients with NSCLC. The benefits of staging PET scans are well established, with improved selection of patients for curative radiotherapy or aggressive chemo-radiotherapy. The large body of literature correlating FDG-PET with nodal pathology in NSCLC makes it rational to use PET for designing mediastinal radiation fields. However, suboptimal image-fusion and a low spatial resolution for PET scans, makes use of PET for defining target volumes for primary tumours questionable. Data on the role of PET scans for radiotherapy planning for limited stage small-cell lung cancer is limited, although the incorporation of FDG-PET positive regions would appear to be reasonable.