Molecular resistance mechanisms affecting the efficiency of receptor tyrosine kinase inhibitors such as gefitinib in non-small-cell lung cancer (NSCLC) cells are not fully understood. Amphiregulin (Areg) overexpression has been proposed to predict NSCLC resistance to gefitinib and we have established that Areg-overexpressing H358 NSCLC cells resist apoptosis. Here, we demonstrate that Areg prevents gefitinib-induced apoptosis in NSCLC cells. We show that H358 cells are resistant to gefitinib in contrast to H322 cells, which do not overexpress Areg. Inhibition of Areg expression by small-interfering RNAs (siRNAs) restores gefitinib sensitivity in H358 cells, whereas addition of recombinant Areg confers resistance in H322 cells. Areg knockdown overcomes resistance to gefitinib and induced apoptosis in NSCLC H358 cells in vitro and in vivo. Under gefitinib treatment, Areg decreases the expression of the proapoptotic protein BAX, inhibits its conformational change and its mitochondrial translocation. Thus, in the presence of Areg, gefitinib-mediated apoptosis is reduced because BAX is sequestered in the cytoplasm. This suggests that treatments using epidermal growth factor receptor (EGFR) inhibitors may be poorly efficient in patients with elevated levels of Areg. These findings indicate the need for inhibition of Areg to enhance the efficiency of the EGFR inhibitors in patients suffering NSCLC.