['This study examined the expression of CDC20 in human non-small cell lung cancer (NSCLC), explored its clinicopathological significance, and evaluated as a potential prognostic marker.', 'A total of 362 cases of NSCLCs were analyzed immunohistochemically on tissue microarrays (TMAs). Additionally, the immunoreactivity of mitotic arrest defective protein 2 (MAD2) was also studied. The clinicopathological implications of these molecules were analyzed statistically.', 'High-level CDC20 protein expression (CDC20-H) was detected in 71 cases (19.6%). Additionally, CDC20-H was correlated with male sex, pT status, pleural invasion, and non-adenocarcinoma (non-ADC) histology. Significant correlation between CDC20 and MAD2 expression was found. NSCLC patients with tumor exhibiting CDC20-H showed significantly shorter 5-year overall survival (P=0.0007). According to subset analyses, CDC20-H was associated with shorter survival than CDC20-L only among ADC patients (P=0.0008), and not among squamous cell carcinoma (SCC) patients (P=0.5100). Importantly, CDC20-H was also identified as an independent prognostic factor in multivariate analysis (P=0.0065).'] Does overexpression of CDC20 predict poor prognosis in primary non-small cell lung cancer patients?