From the County of Uppsala, Sweden, more than 1600 persons with pleural plaques and/or asbestos-related pleural thickening have been seen at the Uppsala University Hospital during a period of about 15 years. During the observation time, 40 patients developed lesions mainly affecting the upper lobes of the lung. They were all men, 41 to 78-years-old, and all had been occupationally exposed to asbestos. The mean latency time from the first exposure was 34 years. The mean width of the apical pleural thickening was 21 mm. In 21 patients the lesions were on the right side, in 15 they were bilateral, and in only four patients was the left side alone affected. Biopsies from the pleura were available in twelve patients and from the lung parenchyma in eight. The biopsies of the lungs all showed varying degrees of asbestosis and of the pleura nonspecific pleuritis. The lesions tended to progress and in all cases except one they were part of a diffuse pleural and parenchymal fibrosis involving the rest of the lung. Consequently, the pulmonary function was impaired, with the vital capacity reduced to an average of 62% and total lung capacity to 68% of the predicted value. In many patients there was contraction of the upper lobe and deviation of the trachea towards the same side. Upper lobe changes are a relatively rare complication of exposure to asbestos but are important to recognise. Other possible causes of upper lobe changes such as tuberculosis must always be excluded before the diagnosis is made.