BACKGROUND: The Will Rogers phenomenon occurs when newer technology allows for more sensitive detection of tumor spread, resulting in stage migration and an apparent improvement in patient survival. We investigated whether use of highly sensitive positron emission tomography (PET) scanning in non-small cell lung cancer has had this effect. METHODS: We performed a retrospective analysis involving 12,395 patients with non-small cell lung cancer in the pre-PET (1994-1998) and PET (1999-2004) periods. Interperiod differences in staging procedures, clinical variables, and patient survival were evaluated. RESULTS: There was a 5.4% decline in the number of patients with stage III disease and an 8.4% increase in the number of patients with stage IV disease in the PET period, corresponding with an increase in PET use from 6.3% to 20.1% (P < .001). The PET period predicted better survival with a hazard ratio (HR) of 0.95 (95% confidence interval [CI], 0.91-0.99) (P = .02). Use of PET was independently associated with better survival in patients with stage III (HR, 0.77; 95% CI, 0.69-0.85) and stage IV (HR, 0.64; 95% CI, 0.58-0.70) disease, but not those with stage I or II disease. CONCLUSION: These data support the notion that stage migration is responsible at least in part for an apparent improvement in survival for patients with stage III and IV non-small cell lung cancer in the PET scan era.