Introduction Tumors might not optimally respond to systemic therapy if minimal effective levels are not reached within the tumor. Erlotinib has mainly been studied in the adjuvant or palliative setting and, therefore, little is known about erlotinib tumor penetration. The purpose of this exploratory study was to investigate lung tumor tissue erlotinib concentrations after neoadjuvant therapy for non-small-cell lung cancer. Patients and Methods Patients were treated preoperatively with erlotinib (150 mg once daily for 3 weeks) up to 48 hours before surgery. Plasma samples were collected during treatment. Surgical resection involved radical resection of the lung tumor and tumor biopsies were frozen directly after surgery. Erlotinib and O-desmethyl erlotinib concentrations in lung tumor tissue and predose plasma were determined using high performance liquid chromatography coupled with tandem mass spectrometry. Results Thirteen evaluable patients were included. The mean plasma and lung tumor tissue erlotinib levels were 1222 ng/mL (SD, 678) and 149 ng/g (SD, 153), respectively. In 2 individual patients, erlotinib and O-desmethyl erlotinib concentrations in lung tumor tissue were detectable up to 13 days and 7 days after erlotinib intake, respectively. Mean erlotinib tissue concentrations extrapolated to a time point directly after intake of erlotinib were approximated at > 200 ng/g tissue, which is greater than the reported half maximal inhibitory concentration (IC50) of wild type epidermal growth factor receptor (EGFR) (183 ng/mL). Conclusion No strong accumulation of erlotinib in lung tumor tissue was observed. Nevertheless, extrapolated intratumoral concentrations during erlotinib therapy were greater than the IC50 of wild type EGFR.