This study examined the reliability and validity of a new measure for evaluating symptoms in patients with chronic obstructive pulmonary disease (COPD): the Breathlessness, Cough and Sputum Scale (BCSS). Designed as a daily diary, the BCSS is a patient-reported outcome measure that asks patients to rate the severity of the three symptoms, each on a 5-point scale; higher scores indicate more severe symptoms. Item scores are summed to yield a total score. Secondary analysis of data were from two multinational trials (n = 629; 765). The BCSS item and total scores exhibited evidence of internal consistency (alpha = 0.70 daily; 0.95 to 0.99 over time) and reproducibility (ICC = 0.77 to 0.88). Correlations (r) with pulmonary function (FEV1 % predicted, PEF) were -0.01 (n.s.) to -0.36 (P < 0.001). Correlations with the St George's Respiratory Questionnaire total and SF-36 Physical Functioning subscale were 0.44 to 0.59 (P < 0.0001). Breathlessness and total scores differentiated patients by disease severity (P < 0.01) and rescue medication use (P < 0.01). Cough, sputum, and total scores increased with sputum volume (r = 0.27, 0.30, 0.31; P < 0.001). Patients for whom treatment was moderately or highly effective reported significant improvements in BCSS scores (P < 0.0001). Results suggest that the BCSS is a reliable, valid, and responsive patient-reported outcome measure of symptom severity in patients with COPD.