In patients with previously-untreated, completely-resected pathologic stage II-III non-small cell lung cancer, 4 months of postoperative cisplatin-based chemotherapy reduces the risk of death by approximately 20%. To date, the only prospectively validated prognostic and predictive factor which can be used to guide clinical practice is pathologic stage. Higher stage patients have a worse prognosis, but derive more benefit from adjuvant chemotherapy. Numerous molecular markers are being developed with the potential to help decide which patients to treat with adjuvant chemotherapy, and which drugs to use. This paper will review the molecular markers which are having immediate impact on treatment decisions in routine practice, and which merit further study in the next generation of adjuvant chemotherapy trials.