The NCCN Clinical Practice Guidelines in Oncology (NCCN Guidelines) allow many systemic therapy options for patients with metastatic non–small cell lung cancer (NSCLC). This analysis uses the NCCN NSCLC Outcomes Database to report on first-line therapy practice patterns and concordance with NCCN Guidelines. The analysis was limited to patients diagnosed with metastatic NSCLC between September 2006 and November 2009 at 1 of 8 participating NCCN Member Institutions. Patient characteristics, regimens used, and guidelines concordance were analyzed. Institutional variation and changes in practice over time were also measured. A total of 1717 patients were included in the analysis. Of these, 1375 (80%) were treated with systemic therapy, most often in the form of a carboplatin-based doublet (51%) or carboplatin-based doublet with targeted therapy (17%). Overall, 76% of patients received care that was concordant with NCCN Guidelines. Among patients with good performance status (n = 167), the most common reasons for not receiving first-line therapy were that therapy was not recommended (39%) or death occurred before treatment (33%). The most common reason for receiving nonconcordant drug therapy was the administration of pemetrexed or erlotinib before its incorporation into the NCCN Guidelines for first-line therapy (53%). Most patients in this cohort received care that was concordant with NCCN Guidelines. The NSCLC Outcomes Database is a valuable resource for evaluating practice patterns and concordance with NCCN Guidelines among patients with NSCLC.