Pulmonary giant cell carcinoma is one of the most highly malignant neoplasms of the lung. Although mixed malignant glandular or squamous components may be associated with a giant cell carcinoma, it is a distinct clinical and morphologic entity. We reviewed cytologic presentations of 6 cases of pulmonary giant ceil carcinoma. Cytologically, the single most characteristic feature of giant cell carcinoma was an extremely large, bizarre cancer cell engulfing numerous leukocytes. The nuclei of these cells showed occasional prominent nucleoli, and the cytoplasm was abundant. Giant cells were also seen in other types of pulmonary carcinoma, but the slant cells of this neoplasm could be differentiated from those encountered in undifferentiated large cell carcinoma and squamous cell carcinoma by the abundant cytoplasm, the presence of markedly enlarged nuclei, prominent nucleoli, and a significant degree of phagocytosis. In conclusion, precise diagnosis and classification of lung cancer is imperative because of proved correlation between cell type and prognosis.