A pathological study was made of lung carcinoma associated with silicosis in about 450 autopsies of silicosis evaluated between 1960 and 1986. There were 48 cases of lung carcinoma; these were evaluated for cell type, cancer site and severity of silicosis. Among 140 autopsies performed there were 25 cases of lung cancer. The highest incidence was 32.5% in mild silicosis, and the lowest incidence was 4.1% in severe silicosis. For all 48 cases, the histologic cell types were squamous cell in 54.2%, small cell in 22.9%, adenocarcinoma in 14.6% and large cell in 8.3%. Adenocarcinoma only occurred peripherally while squamous cell carcinoma was more prevalent in larger airways. More tumors were observed in right versus left lung, with no difference for upper or lower lobes. Right, upper and larger airway carcinomas were noted more in mild silicosis; left, lower and peripheral carcinomas were noted more in medium and severe silicosis. Stem and lobar bronchi were more common tumor sites in mild silicosis, and segmental bronchi had more tumors in medium and severe disease. When progressive massive fibrosis (PMF) was present, most tumors were observed in segmental bronchi leading to the PMF. Peripheral tumors were also associated with PMF when it was present. Three cases of scar cancer arising in scar tissues of PMF were noted. Diffuse interstitial fibrosis was commonly observed; five cases of lung cancer were noted in such cases. The authors conclude that there is a close relationship between pathological changes in lung tissue due to dust exposure and occurrence of lung carcinoma.