Rationale: Muscle wasting in Chronic Obstructive Pulmonary Disease is associated with a poor prognosis and is not readily assessed by measures of body mass index (BMI). BMI does not discriminate between relative proportions of adipose tissue and lean muscle and may be insensitive to early pathologic changes in body composition. Computed tomographic (CT) based assessments of the pectoralis muscles may provide insight into the clinical significance of skeletal muscles in smokers. Objectives: We hypothesized that the objective assessment of the pectoralis muscle area on chest CT scans provides information that is clinically relevant and independent of BMI. Study Design: Data from the ECLIPSE study (n=73) was used to assess the relationship between pectoralis muscle area and fat-free mass. We then used data in a subset (n=966) of larger cohort, the COPDGene study, to explore the relationship between pectoralis muscle area and COPD-related traits. Measurements and Main Results: We first investigated the correlation between pectoralis muscle area and fat-free mass using data from a subset of participants in the ECLIPSE study. We then further investigated pectoralis muscle area in COPDGene and found that higher pectoralis muscle area values were associated with greater height, male sex and younger age. On subsequent clinical correlation, pectoralis muscle area was more significantly associated than BMI with COPD-related traits, including spirometric measures, dyspnea and 6-minute walk distance (6MWD). For example, on average each 10 cm2 increase in pectoralis muscle area was associated with a 0.8 unit decrease in BODE (95% Confidence Interval: -1.0 to -0.6, p<0.001). Furthermore, statistically significant associations between pectoralis muscle area and COPD-related traits remained even after adjustment for BMI. Conclusions: CT derived pectoralis muscle area provides relevant indices of COPD morbidity that may be more predictive of important COPD-related traits than BMI. However, the relationship with clinically relevant outcomes such as hospitalization and death requires additional investigation. Pectoralis muscle area is a convenient measure that can be collected in the clinical setting in addition to BMI.