Bronchiolitis obliterans organizing pneumonia (BOOP), also known as cryptogenic organizing pneumonia, has mainly been described in patients with breast cancer who received radiotherapy after breast-conserving surgery. In this rare case, a 70-year-old man with left apical squamous lung cancer developed BOOP after radiotherapy and only one cycle of concomitant chemotherapy.This case report draws attention to the development of this syndrome in the unusual setting of lung cancer, advising prompt steroid treatment when diagnostic images reveal the characteristic signs of the disease.