One hundred sixty-five nonsmoking systemic sclerosis patients were evaluated by pulmonary function testing. Restrictive lung disease and an isolated reduction of the diffusing capacity of carbon monoxide were the most frequent abnormalities. Patients with the CREST syndrome (calcinosis, Raynaud's phenomenon, esophageal dysmotility, sclerodactyly, and telangiectasias) had a similar frequency and severity of pulmonary involvement compared with the patients who had diffuse scleroderma. CREST syndrome patients with restrictive lung disease rarely had the anticentromere antibody and had more skin and joint involvement of their hands, compared with other CREST syndrome patients. Dyspnea and rales were most commonly found in patients with restrictive lung disease. Fibrosis, shown on chest radiograph, and pulmonary function abnormalities correlated poorly with each other. Dyspnea was associated with restrictive disease, and rales were more commonly found in patients with fibrosis. Patients with a restrictive abnormality had the worst prognosis, with a 5-year survival rate of 58%, although death from pulmonary causes was uncommon. Comparison of these nonsmoking patients with 137 scleroderma patients who smoked, seen during the same time period, revealed more frequent and severe obstructive changes in smokers. Smoking patients with restrictive lung disease had more severe disease than nonsmoking patients. The single breath diffusing capacity for carbon monoxide was significantly decreased in the patients who smoked compared with the nonsmokers. These data confirm that pulmonary function abnormalities are common in patients with systemic sclerosis including CREST syndrome. Smoking appears to have an additive deleterious effect on pulmonary function and should be strongly discouraged.