The purpose of this trial (Lung Cancer Study Group [LCSG] 853) was to perform a comparative study of immediate combination chemotherapy (cyclophosphamide, doxorubicin, cisplatin [CAP]) vs delayed combination chemotherapy (CAP) administered at the time of first systemic relapse in patients with completely resected stage II and stage III non-small cell cancer of the lung. We randomly assigned 188 patients with resected stage II or stage III non-small cell lung cancer of the lung (squamous, 53%; nonsquamous, 47%) to receive either immediate or delayed combination chemotherapy. Careful intraoperative staging was performed in all patients. Before randomization, patients were stratified according to stage-II (hilar nodes positive) vs III (mediastinal nodes positive or T3)-and histologic features (squamous vs nonsquamous), Ninety-four patients were randomized to receive immediate CAP vs 94 patients randomized to receive delayed CAP. Prognostic variables such as extent of disease, histologic features, sex, race, TN status, and Karnofsky performance status were equally distributed between randomized groups. The treatment groups differed with respect to greater than 10% weight loss. Forty-one percent of patients had stage II disease and 59% of patients had stage III disease. Median time to recurrence (19.5 months) and survival (32.7 months) did not differ between treatment groups. Immediate combination chemotherapy was associated with a 12% reduction in risk of recurrence and an 18% reduction in risk of death, although these rates were not statistically significant. Histologic features, sex, race, Karnofsky performance status, nodal status, and weight change were associated with higher risks of recurrence.