PURPOSE: Spiculation pathologically correlated with irregular fibrosis, localized lymphatic spread of tumor, or an infiltrative growth pattern of tumor, and the spiculation was Observed in malignant mass. But the spiculation was also observed in benign mass, particularly in tuberculoma. We retrospectively reviewed the length of spiculation under the hypothesis that the length of spiculation could be one of differential diagnostic points between lung cancer and tuberculoma. MATERIALS AND METHODS: We studied thirty seven patients (27 men and 10 women) ranging in age from 35 to 80 years (mean, 60 years). Analysis of spiculation included (a) the number of spicules (b) the mean length of spicules (c) the mean length of the longest spicule (d) the percentage of the mean length of spicules to the longest diameter of mass (e) the percentage of the mean length of spicules to the shortest dia, meter of mass. RESULTS: The mean length of spicules of tuberculoma was 13.8 mm (S. D. 6.7) and that of lung cancer was 5.7 mm (S. D. 3.5). The percentage of the mean length of spicules to the longest diameter of tuberculoma was 63.6% and that of lung cancer was 13.7%. The percentage of the mean length of spicules to the shortest diameter of tuberculoma was 90.4% and that of lung cancer w~s 18.3%. CONCLUSION: It is hard to differentiate lung cancer from tuberculoma on the basis of the spiculation being present or not, but we suggest that the longer spiculation be more highly suggestive of tuberculoma rather than lung cancer. The length of spiculation may help us differentiate lung cancer from tuberculoma.