OBJECTIVES: This national population-based retrospective study aimed to evaluate the relative effectiveness of adding erlotinib to gemcitabine with pancreatic cancer patients compared to gemcitabine in real clinical practice. METHODS: Patients was identified retrospectively using Korean National Health Insurance claims database who pancreatic cancer (ICD-10: C25) who initiated chemotherapy with gemcitabine or erlotinib between January 1, 2007 and December 31, 2012. To be included in the study population, patients were required to have a history of intervention for histologic or cytologic diagnosis within one year before chemotherapy. For homogeneity, patients were excluded if they have diagnosed with other cancers where gemcitabine is indicated or prior radiotherapy or surgical treatment. RESULTS: A total of 4,267 patients were included. Overall survival was not significantly longer in patients treated with gemcitabine/erlotinib (median 6.77 months for gemcitabine/erlotinib vs.