OBJECTIVE We evaluated bone mineral density and phosphorus calcium status in patients with chronic lung diseases. METHODS A prospective study was conducted in 58 patients (43 men and 15 women, mean age 44 years, age range 16-68 years) who were classed in three groups: chronic obstructive diseases (25 patients), cystic fibrosis (19 patients), and other lung diseases (14 patients). Fifteen percent of the patients were receiving corticosteroid therapy. Bone mineral density of the lumbar spin and the femoral neck was measured. RESULTS Serum calcium, phosphate, creatinine, osteocalcin and parathyroid hormone were normal. The 25-hydroxyvitamin D (normal=9-40 ng/ml) level was in the lower limits of normal (12 ng/ml) and was severely decreased in 12 patients (<7 ng/ml). CONCLUSIONS Chronic lung disease can lead to osteoporosis. Corticosteroids, low vitamin D level, sedentary lifestyle, smoking, and in cystic fibrosis nutritional deficiencies, delayed puberty and hypogonadism are risk factors. Bone density must be measured in order to prevent and treat osteoporosis.