Diagnosis of lung cancer in 47 patients aged younger than 40 years was delayed as a result of misdiagnosis, accounting for 70.1% of all cases of lung cancer in those aged less than 40 years treated in PUMC Hospital in the same period. Pulmonary tuberculosis and tuberculous pleurisy were diagnosed in 26 cases (55.3%). Pulmonary inflammation was suspected in 24 cases (51.1%). The delay in diagnosis was one to three months in 28 cases and longer than 3 months in 19 cases. Twenty-eight (59.6%) of the 47 patients underwent surgery, including exploratory thoracotomy (21.4%) and pneumonectomy (40.9%). The five-year survival rates in the resectable group and in the non-surgical group were 31.6% and 5.3%, respectively. We recommend that accessory examinations should be performed wherever possible in younger patients with suggestive pulmonary nodules in order to collect sufficient evidence to confirm or rule out the diagnosis of lung cancer and thereby reduce the rate of misdiagnosis in such younger people.