Background:Accurate staging of lung cancer is paramount for directing treatment. After an internal audit suggested a higher than expected rate of synchronous multiple primary lung cancers (SMPLC), we have sought to evaluate the prevalence of SMPLC at our single, large academic center. Methods:From January 2019 to September 2019, patients with non-small cell lung cancer who underwent surgical resection were retrospectively reviewed. Clinical characteristics, pre- and post-op imaging, 30-day morbidity and mortality, as well as pathological findings were reviewed. SMPLCs were defined using modified Martini criteria. Results:Among 83 patients who underwent surgical resection for primary lung cancer with the intention of cure, 17 (20.5%) had pathologically confirmed SMPLC's, 53 (64%) were single primary lung cancers, and 13 (16%) had metastatic lesions from primary lung cancer or extra-thoracic cancers. Mean length of stay was 2 days with no mortalities. Of the SMPLC group, 9 (53%) had previous extra-thoracic neoplasms, compared with 8 (15%) in the single primary group. Four (24%) had a history of resected lung cancers more than 2 years previously, and were participating in lung cancer surveillance programs. Conclusions:The rate of SMPLC at our institution appears to be considerably higher than traditionally reported. Failure to recognize the high incidence of synchronous primary lung cancers exposes patients to the risks of under treatment and poor outcomes.