A 47-year-old woman with non small cell lung cancer underwent a F-FDG PET/CT scan to assess disease progression after she developed a second non small cell lung cancer. Seven years earlier, she had a left lower lobectomy adjuvant chemoradiation for stage IIIA disease with microscopic subcarinal nodal involvement. There was markedly increased FDG uptake into brown fat in the soft tissues of the posterior lateral head neck, both supra- and infra-clavicular fossae and the right costovertebral region. Brown fat FDG uptake in the left costovertebral region was absent below the left third rib, which corresponded to the radiation field.