One of the extrapulmonary effects of chronic obstructive pulmonary disease (COPD) is osteoporosis. Osteoporosis is characterized by a low bone mineral density (BMD) and microarchitectural deterioration. Most studies in COPD patients use dual-energy X-ray absorptiometry (DXA) only to determine osteoporosis; therefore, microarchitectural changes without a low BMD are missed. The aim of this study was to determine the prevalence and correlates of osteoporosis in COPD patients based on DXA, spinal X-rays, and combinations thereof. DXA and spinal X-rays were obtained and pulmonary function tests, body composition, 6-minute walking distance, medical history, and medication use were assessed in 255 clinically stable COPD outpatients of a large teaching hospital in the Netherlands. Half of all patients had radiologic evidence of osteoporosis. Combining the results of DXA with spinal X-rays augmented the proportion of COPD patients with osteoporosis compared with both methods separately. The prevalence of osteoporosis was not significantly different after stratification for Global Strategy for the Diagnosis, Management, and Prevention of COPD (GOLD) stage. Most patients with osteoporosis did not receive pharmacologic treatment. Age, body mass index (BMI), and parathyroid hormone (PTH) level were significant independent correlates for osteoporosis. Chest physicians should be aware of the high prevalence of osteoporosis in patients with COPD, even in the presence of a low GOLD score, as well as especially in elder COPD patients with a low BMI and/or an increased PTH level. © 2011 American Society for Bone and Mineral Research.