Although muscle loss is thought to be a prognostic factor in chronic obstructive pulmonary disease (COPD), its determinants remain unclear.To verify the hypothesis that fat-free mass (FFM) and fat mass (FM) are associated with the extent of emphysema in COPD patients.A total of 112 stable, male current or ex-smokers with or without COPD attending a secondary care specialist COPD clinic were studied. FFM and FM were measured by bioelectrical impedance analysis. We also assessed the nutrition status, muscle strength by the handgrip test, exercise tolerance by the 6-minute walking test, airflow limitation and diffusion capacity, the extent of emphysema by high-resolution CT scan, systemic inflammation status using C-reactive protein, and a lipid-related hormone (adiponectin).The FFM index (FFMI), which was defined as the FFM divided by the square of the body height, was significantly correlated with age, the total number of lymphocytes, handgrip strength, distance on 6-minute walking, airflow limitation, diffusion capacity, extent of emphysema, and C-reactive protein. On multivariate analysis, the FFMI was associated with handgrip strength and inversely correlated with the extent of emphysema. The FM index (FMI) was positively correlated with pack-years, and was inversely correlated with the extent of emphysema and concentrations of adiponectin.The extent of emphysema was correlated with skeletal muscle loss and also the FM.