This study was designed to find the differentiated phenotype and its clinicopathological significance in pulmonary large cell carcinoam (PLCC) by immunohistochemical methods using a panel of antibodies related to the phenotype differentiation: high molecular weight cytokeratin, low molecular weight cytokeratiin, secretory component, chromogranin A and synaptophysin in 60 cases of PLCC. The results demonstrated that all cases of PLCC possessed monophasic, biphasic and triphasic phenotype differentiation features respectively, including squamous (4 cases), adenomatous (20 cases), neuroendocrine (19 cases), adenosquamous (11 cases); and the the coexistence of adenomatous, squamous and neuroendocrine (6 cases). The median survival time was different between patients with various differentiated phenotypes of PLCC. There was a statistically significant difference (P < 0.05) in survival between neuroendocrine and adenomatous phenotypes. The results of this study implies that: (1) PLCC expressed different phenotypes of differentiation, (2) phenotypes of neuroendocrine differentiation has a poor prognosis, (3) it is necessary to classify PLCC according to the phenotype differentiation.