Background: Afatinib is an irreversible ErbB family blocker that inhibits EGFR with activating mutations as well as the T790M resistance mutations. This study investigated efficacy, safety and dosage of afatinib under a Named Patient Use (NPU) program in a single institution. Methods: We analyzed 60 patients with stage IV NSCLC that had been treated with ≥ 1 platinum based chemotherapy, and with activating EGFR mutation or disease control for ≥ 6 months with prior EGFR-TKIs (gefitinib or erlotinib). Two received afatinib as 3rd line treatment, 27 as 4th line, 19 as 5th line and 12 as ≥ 6th line. Mutations were detected in 11 (exon 19 deletion) and 7 (L858R) cases. No activating mutation was found in 19 cases, and EGFR status was not studied in 23 cases. Results: Thirteen patients achieved PR, 33 SD, 12 PD, and 2 not-evaluable resulting in a response rate of 21.7% and a disease control rate of 76.7%. Median PFS was 5.2 months (95% CI, 4.1 to 6.4 months) and median OS was 13.4m (95% CI, 12.6 to 14.2). Toxicities leading to drug discontinuation were experienced by 4 patients (6.7%). Grade 3 diarrhea occurred in 10 patients (16.7%), and dosage reductions of afatinib were required in 35 patients, to 40mg in 25 and to 30mg in 10 cases. The PFS and OS were significantly longer for patients whose dosage of afatinib were reduced to 40 or 30 mg, compared to patients without dosage reduction (7.5 vs 3.1m and 18.0 vs 9.1m, respectively, p<0.05). Conclusions: Aggressive dosage reduction should be considered in the course of treatment with afatinib.