RATIONALE: Chronic obstructive pulmonary disease (COPD) patients are at increased risk of osteoporosis. Osteoporosis is under diagnosed and under treated in these patients and the underlying mechanisms remain unclear. To date, screening recommendations for osteoporosis in COPD patients are not available. OBJECTIVES: To examine the prevalence of drug treatment of bone abnormalities as well as the clinical determinants of osteoporosis in COPD. METHODS: COPD patients (n=554) consecutively entering pulmonary rehabilitation were included in this cross-sectional study. Medical history, current medication use, smoking status, lung function, bone mineral density, body composition and other clinical characteristics were assessed before entering pulmonary rehabilitation. Univariate- and multivariate multinomial logistic regression analyses were used to determine correlates of osteoporosis. MAIN RESULTS: Twenty-one percent of patients had osteoporosis and 41% had osteopenia. Osteoporosis was pharmacologically under treated (82% of osteoporotic patients were not receiving bone medication). Independent predictors of osteoporosis were cachexia (OR: 12.1; 95%CI: 4.5-32.7; p<0.001), age between 55 and 65 years (OR: 6.0; 95%CI: 2.2-16.3; p<0.001) and over 65 years (OR: 11.7; 95%CI: 4.1-33.1; p=<0.001). Overweight (OR: 0.1; 95%CI: 0.05-0.4; p=0.001) and obesity (OR: 0.78; 95%CI: 0.02-0.4; p=0.002) showed a substantial protective effect. CONCLUSIONS: The majority of COPD patients with osteoporosis entering pulmonary rehabilitation did not receive pharmacological treatment for osteoporosis. Cachectic COPD patients should be screened for osteoporosis, especially when over 55 years of age.