Background Postoperative mortality is the most commonly reported surgical quality measure. However, such metrics may be incapable of identifying performance outliers. The purpose of this study was to compare different measures of postoperative mortality after lung cancer resection using a large multiinstitutional database. Methods Data were extracted for lung cancer resection patients from the linked Surveillance Epidemiology and End Results-Medicare Registry (2006 to 2010), which provides detailed and longitudinal information about Medicare beneficiaries with cancer. Four definitions of postoperative mortality were evaluated: in-hospital, 30-day, perioperative, and 90-day. Hierarchical regression models were used to estimate mortality risk at 30 and 90 days, and provider quality was assessed by comparing observed versus expected mortality. Results We identified 11,787 lung cancer resection patients from 686 hospitals. The median age was 74 years, and 52% of patients were treated with open lobectomy. Although 30-day, perioperative, and in-hospital mortality rates were between 3% and 4%, 90-day mortality was almost double (6.89%). Clinical variables associated with 90-day mortality included sex, preexisting comorbidities, and procedure type. There were no statistically significant differences in 30-day or 90-day mortality rates among providers. Conclusions Currently reported measures of in-hospital and 30-day postoperative mortality do not adequately represent a patient's true mortality risk as mortality almost doubles by 90 days. Because of low occurrence rate and variable provider volumes, neither 30-day nor 90-day mortality is a suitable quality indicator for lung resection.