Lumican is a member of a small leucine-rich proteoglycan family and is highly expressed in several types of cancer cells and/or stromal tissue. Lumican expression in the cytoplasm in advanced colorectal cancer correlates with poor patient prognosis. The expression of lumican in stromal tissues is associated with a high tumor grade, a low estrogen receptor expression level, and young age in breast cancer and is associated with tumor invasion and advanced stage in pancreatic cancer. In this study, we examined the expression and role of lumican in lung cancer including adenocarcinoma (ADC) and squamous cell carcinoma (SqCC). Immunohistochemically, lumican was weakly expressed in vascular smooth muscle cells, perivascular and peribronchial connective tissues and bronchial epithelium of normal lung tissues. In lung cancer tissues, lumican was localized in the cytoplasm of cancer cells and/or stromal tissues adjacent to cancer cells. In ADC, the expression level of lumican in cancer cells correlated with pleural invasion and larger tumor size, but that of lumican in stromal tissues did not correlate with clinicopathological factors. In SqCC, the expression level of lumican in cancer cells correlated with formation of a keratinized pattern, and stromal lumican expression correlated with vascular invasion. In SqCC and ADC, the expression level of lumican in cancer cells did not correlate with patient prognosis. In lung cancer cell lines, lumican mRNA and protein were expressed in LC-1/Sq and EBC-1 cells established from SqCC, and A549, RERF-LC-KJ and PC-3 cells from ADC. The molecular weight of lumican extracted from the cytoplasm of lung cancer cells differed from that in the culture medium owing to glycosylation of the protein. These findings suggest that the expression pattern and the glycosylated type of lumican in cells and stromal tissues correlate with the aggressiveness of lung SqCC and ADC.