A 36-yr-old woman complaining of cough and body weight loss at a health checkup and referred to us after an abnormality was noted on the chest X-ray was diagnosed with clinical stage IV (cT2N3Ml) non-small-cell lung cancer (adenocarcinoma). She received three courses of chemotherapy. The response to treatment was stable disease. She was subsequently enrolled in a clinical trial of S-1, a new oral fluoropyrimidine anticancer drug, and received a total of 22 courses of S-1 over a period of 2 yr 5 mo. At the end of treatment, she was classified as having a partial response. A bronchoscopic biopsy disclosed no cancer cells. Remission continued for 1 yr 7 mo after treatment. The patient died of primary disease 8 yr after the initiation of treatment with oral S-1. Non-small-cell lung cancer was approved as a new indication of S-1 in 2004 in Japan, but the number of patients receiving it for this indication remains limited. Here, we describe our experience with a patient with adenocarcinoma of the lung who survived for a prolonged period after treatment with S-1. Our findings suggest that S-1 is effective for the treatment of non-small-cell lung cancer.