A systematic review of the evidence for postoperative chemotherapy in completely resected nonsmall cell lung cancer was conducted. Seven meta-analyses and 25 randomized trials met the pre-defined eligibility criteria for the review. The evidence indicates that postoperative platinum-based chemotherapy improves survival compared with surgery alone; for patients with a good performance status who are fit enough for chemotherapy, the survival benefits strongly outweigh the adverse effects of treatment. To date the trials restricted to stage IB or II disease have obtained the greatest survival benefits with postoperative platinum-based chemotherapy. The evidence does not support the use of postoperative radiotherapy with chemotherapy.