Pulmonary disease is a well-known complication of Type 1 Gaucher disease (GD), although its incidence is not well established and its severity varies. The purpose of this study was to determine the frequency and extent of pulmonary involvement in patients with GD. Pulmonary involvement was assessed by history, physical examination and chest radiograph in 150 consecutive patients with Type 1 GD presenting at a specialized center for genetic diseases. Five patients were noted to have clinical evidence of pulmonary involvement. Full pulmonary function tests were performed in these five patients and in an additional 13 patients randomly selected from the remaining 145. Many of the 18 patients also underwent radionuclide body imaging with 67 Gallium citrate and 111Indium-tagged leucocyte scans, as well as incremental cardiorespiratory exercise tests. Lung biopsies were available in two patients with lung disease, and a second examination of lung tissue was performed in one of these two patients post-mortem. Clinical lung disease was detected in five patients. All five had dyspnea, diffuse infiltrates, restrictive impairment and low single breath CO diffusing capacity (DLCOSB). Two of these patients underwent exercise testing and showed abnormalities consistent with lung disease (ventilatory limitation, excessive ventilation and increased dead space) as well as decreased VO2 max. and anaerobic threshold (AT). In contrast, in the other 13 patients, physical examination, chest radiographs and pulmonary function were normal (except for a low DLCOSB in one patient). Responses on exercise testing (performed in six of the 13 patients) were consistent with a circulatory impairment (decreased VO2 max. and AT). Our study found that <5% of patients with Type 1 GD have clinical interstitial lung disease. In addition, we found that some patients, without evident lung involvement, may experience limitations in physical exertion and are easily fatigued; this is attributable to impaired circulation.