Calcification is known to be an important factor in differentiating benign from malignant pulmonary nodules. From a review of CT scans of 236 patients with lung cancer, 36 patients(15.3%) showing obvious calcification within the mass were analyzed retrospectively in terms of clinical, radiological, and pathological findings. Prevalences of calcification in each cell type were 18.6%(24/129) for squamous cell carcinoma, 14.7%(5/34) for small-cell carcinoma and 8.3%(5/60) for adenocarcinoma. The distribution of calcification within the lesions were peripheral in 23 patientss(63.9%), scattered in 11(30.5%), and central in 2(5.6%). Previous histories of pulmonary tuberculosis were identified in 11 patients(30.5%). Our data sugest that prevalence of calcification on CT scans in the differential diagnosis of benign from malignant lung lesions should be accepted differently from that on plain radiograph.