Clinical lung cancer staging is an important basis for choosing treatment modalities and prognosing outcomes. However, it is not always accurate. We reported an interesting process of clinically staging in a case with lung cancer. According to admission computer tomography findings, he was preliminarily diagnosed as stage IV with nonprimary-tumor lobe metastasis and chest wall invasion. Computer tomography findings after accidental pneumothorax resulting from percutaneous puncture biopsy and positron emission tomography findings denied the chest wall invasion and nonprimary-tumor lobe metastasis. His diagnosis was revised as stage IIa that was confirmed subsequently by histological staging after surgery and follow-up. Our experiences indicate computer tomography scanning after artificial pneumothorax is a useful tool for identifying whether or not chest wall is invaded directly by an adjacent tumor, and positron emission tomography scanning needs to be considered for accurately evaluating the nature of concurrent pulmonary nodules in patients with lung cancer.