Objective: To analyse the microsatellite instability (MI) and loss of heterozygosity (LOH) in non-small cell lung cancer (NSCLC). Methods: MI and LOH at chromosome 17 were checked in 35 cases of NSCLC tumor-normal paired tissues using four microsatellite markers TP53 (17p13.1), THRA1 (17q11.2-12), D17S579 (17q12-21) and D17S855 (17q21) by PCR based analysis. Mutations of P53 exons 5-8 were also tested using PCR-single strand conformation polymorphism (PCR-SSCP) and PCR-denaturing gradient gel electrophoresis (PCR-DGGE) analysis. Results: 22 of 35 tumors (62.8%) displayed MI or LOH. 14 tumors (40.0%) exhibited MI, 11 tumors (31.4%) exhibited LOH, while 3 tumors (8.6%) exhibited MI and LOH concurrently. 23 tumors (65.7%) exhibited P53 gene mutations. The frequency of MI or LOH was obviously higher in the early-stage (stages I and II, 78.9%) than in the advanced-stage (stage III, 43.8%). However, the frequency of MI or LOH had no difference either between high-grade (75.0%) and low-grade (52.6%) differentiated NSCLC or between the tumors with P53 mutations (59.1%) and those without P53 mutations (69.2%). No relationship was observed between the presence of MI or LOH and the histologic subtype of NSCLC. Conclusion: The results suggest that MI and LOH at chromosome 17 may play a alterations on chromosome 17 in tumors of non-small cell lung cancer (NSCLC). In addition, studies reported contradictory results concerning the incidence of these alterations and the relationship between these genetic alterations and the clinical behavior of NSCLC. The aim of this study was to investigate the incidence of MI and LOH at chromosome 17 in tumors of patients with NSCLC and its association with clinical and histologic features of NSCLC.