We investigated the clinical significance of p16 abnormalities (mutations by sequencing and hypermethylation by methylation-specific PCR) in 52 radically resected stage I-II non-small cell lung cancers (NSCLCs). P16 abnormalities were detected in 20 (38%) patents (point mutations in 4 (8%) and promoter hypermethylation in 16 (31%) cases. No correlation was found between p16 abnormalities and various clinicopathologic factors, including sex, histological type of tumor and TNM (I vs. II) stage. The multivariate analysis of survival was performed using the Cox proportional hazard model. When the types of 16 inactivation were analyzed, p16 hypermethylation rather than point mutation was associated with poor Prognosis. The presented results prompt the conclusion that hypermethylation of p16 is the major mechanism for p16 gene inactivation in early stage NSCLC and could be a useful molecular marker for the prognosis.