Tumor regression was reported in 20-30% of patients with inoperable non-small-cell lung cancer (NSLC) following standard first-line chemotherapy. Clinical trials with second-line gefitinib (Iressa) showed a strikingly high response in patients with mutated EGFR. However, clinical experience with gefitinib as first-line therapy had been limited to small-scale trials mostly among subjects of Asian origin. Our study was not associated with the drug manufacturer and included 25 chemotherapy-naive patients with mutated EGFR inoperable lung adenocarcinoma. Standard dose was 250 mg/day. Complete response was observed in 1 patient (4%), partial--11 (44%), sustained stabilization--13 (52%); median time until tumor progression--186 days. Median overall survival failed to be registered within the duration of the study. Among most frequent side-effects were skin rash (19; 76%) and diarrhea (14; 56%): marked side-effect -toxicity grade III (4; 16%). Gefitinib appeared highly efficient and tolerable and may be recommended as first-line treatment of mutated EGFR inoperable NSLC.