We have evaluated CYFRA 21-1 serum level variations as an indicator of tumor response and survival in 44 consecutive patients with locally advanced non-small cell lung cancer (NSCLC) treated with induction chemotherapy (IC). Irrespective of the initial CYFRA 21-1 serum concentration, a more than 65% decrease in the serum level after the first chemotherapy course was significantly predictive of an objective tumor response (p = 0.0022). In addition, a more than 80% decrease in this level significantly predicted a better disease-free survival (p = 0.039). In patients with initial CYFRA 21-1 serum levels > 3.3 ng/mL (n = 29), a more than 80% decrease after the first IC course was the most significant predictor of overall survival (p = 0.025) in a Cox analysis including initial staging, tumor response and surgery. We conclude that early monitoring of CYFRA 21-1 serum levels may be a useful prognostic tool for tumor response and survival in stage III NSCLC patients treated by induction chemotherapy.