BACKGROUND: The present study aims to give a detailed overview of day-to-day practice in the systemic treatment of NSCLC stage IIIB/IV and its clinical outcomes in six large teaching hospitals in the Netherlands in the period 2008-2012. METHODS: A retrospective observational cohort study was conducted in the Care for Outcome registry. Patients diagnosed with stage IIIB/IV NSCLC were included and drug data were collected. Outcomes included percentage of patients treated with systemic treatment, percentage of different first line treatment options, survival, and number and percentage of switches, dose reductions (<80% of the initial dose), and early discontinuation (<4 cycles). Descriptive analyses were conducted per hospital, year of diagnosis and several patient characteristics. Predictors for early discontinuation were explored in a logistic regression model. RESULTS: Overall, 47,9% of 2158 patients that were included received systemic treatment and 33,7% of those received second line treatment. Treatment frequencies were different between age categories, disease stage, PS and hospital (p<0.001). Half of the patients received <4 cycles and dose reductions were found for 20% of all patients. Interhospital differences were observed for early discontinuation and the number of switches. PS2-3 was associated with early discontinuation (OR 1.97 (p=0,007). Median survival was not different between hospitals and years of diagnosis. DISCUSSION: We provided detailed overview of day-to-day systemic treatment of NSCLC for six hospitals that (a) can fuel interhospital discussion to streamline treatment towards best practice and (b) can serve as reference data for follow-up of the adoption of novel systemic treatment options for advanced lung cancer.