Comprehensive estimates of forest carbon (C) mass and respiration require measurements of all C pools, including coarse woody debris (CWD). We used inventory and chamber-based methods to quantify C mass and the annual respiratory C loss from CWD and other major ecosystem components for a deciduous forest in the upper Great Lakes region. Coarse woody debris mass (MCWD, 2.2 Mg C/ ha) was less than that of soils (104.1 Mg C /ha) and boles (71.7 Mg C /ha), but similar to that of leaves (1.8 Mg C /ha). Coarse woody debris respiration (RCWD) increased with temperature and water content, with differences in RCWD among decay classes due to variation in water content rather than to variable sensitivity to environmental conditions. Sensitivity of RCWD to changing temperature, evaluated as Q10, ranged from 2.20 to 2.57 and was variable among decay classes. Annual CWDrespiration (FCWD, 0.21 Mg C /ha /year) was 12% of bole respiration, 8% of leaf respiration, and 2% of soil respiration. The CWD decomposition rate-constant (FCWD/MCWD) in 2004 was 0.09 /year. When compared to the average annual ecosystem C storage of 1.53 Mg C /ha /year, FCWD represents a small, but substantial flux that is expected to increase over the next several decades in this maturing forest.