OBJECTIVE Although surgical resection alone is considered adequate treatment in stage IB non-small-cell lung cancer (NSCLC), long-term survival is not satisfactory and the recurrence rate is quite high. The validity of postoperative chemotherapy at stage IB in terms of disease-free and overall survival was assessed in a randomised trial. METHODS The trial was designed as a randomised, two-group study with postoperative adjuvant chemotherapy versus surgery alone as control group. All patients had stage IB disease (pT2N0) assessed after a radical surgical procedure. Chemotherapy consisted of treatment with cisplatin (100 mg/m(2) on day 1) and etoposide (120 mg/m(2) on days 1--3) for a total of six cycles. RESULTS Between January 1988 and December 1994, 66 patients were included in the study. Thirty-three belonged to the adjuvant chemotherapy group and 33 to the control group. Groups were homogeneous for conventional risk factors. There was no clinical significant morbidity associated to chemotherapy. Patients were followed for a minimum period of 5 years. The rates of locoregional recurrence and distant metastases were 18 and 30%, respectively, in the adjuvant chemotherapy group and 24 and 43%, respectively, in the control group. The 5-year disease-free survival rates were 59% in the adjuvant group and 30% in the control group (P = 0.02). The difference in the Kaplan--Meier survival between the groups was significant as assessed using the log-rank test (P = 0.04). CONCLUSIONS Our results suggest that adjuvant chemotherapy may reduce recurrences and prolong overall survival in patients at stage IB NSCLC deemed radically operated. Despite being difficult to accept, the use of adjuvant chemotherapy might have better long-term results.