Some patients with cystic fibrosis have reduced pulmonary volumes, indicating a restrictive pattern of pulmonary disease. We identified ten patients with pulmonary functional evidence of restriction among 158 patients with cystic fibrosis followed at the University of California San Diego Medical Center in 1984 and 1985. We characterized the radiographic, pulmonary functional, and clinical characteristics of these restricted patients compared to matched nonrestricted patients. Pulmonary volumes were measured by three different techniques: plethysmography; nitrogen washout; and radiography. Except for plethysmographic pulmonary volumes, there were no significant differences between the matched restricted and nonrestricted patients. Radiographic pulmonary volume tended to overestimate gas volume measured by the other techniques. Differences among these techniques (thought to represent air-space filling) correlated best with radiographic evidence of air trapping and bronchial markings and not with parenchymal lesions. Serial pulmonary function tests demonstrated changes in pulmonary volume in several patients and a trend toward improvement in pulmonary volume in the restricted patients over time. We conclude that restricted pulmonary function does not necessarily indicate more severe disease in patients with cystic fibrosis and may be reversible in some. The mechanism of restriction may be related more to radiographic evidence of airway disease than to parenchymal abnormalities.