Idiopathic pulmonary fibrosis (IPF) is strongly associated with lung cancer compared with the general population. However, other types of idiopathic interstitial pneumonia (IIP) are rarely associated with lung cancer. We describe a case of a primary lung cancer associated with IIP other than IPF, which was considered to be nonspecific interstitial pneumonia (NSIP), and NSIP disappeared spontaneously after treating the primary lung cancer.