A cohort of 1,117 asbestos insulation workers was established in 1963 and has been prospectively followed since then. Chest X-ray abnormalities detected at the initial medical examination, and interpreted according to the International Labour Office Classification of Radiographs of Pneumoconioses are reported in this paper. The prevalence of all radiographic abnormalities (pleural and pulmonary) increased with duration from onset of asbestos exposure. A positive smoking history was associated with a significantly higher prevalence of small irregular opacities indicating interstitial pulmonary fibrosis. Such an association was not found for pleural fibrosis. The possible mechanisms which underlie the effect of smoking on asbestos-induced interstitial fibrosis seem to be of much less importance in the development of pleural fibrosis. Progression of radiographic changes over the 20-year interval 1963-1983 will be separately reported as will the predictive significance of these changes.