Disturbed sleep is reportedly common in chronic obstructive pulmonary disease (COPD), but the impact of quality of sleep on health-related quality of life (HRQL) has not been previously investigated in these individuals. The purpose of this study was to assess the impact of quality of sleep on HRQL in patients with COPD. In 30 clinically stable patients with moderate to very severe COPD, we evaluated subjective sleep quality using the Pittsburgh Sleep Quality Index (PSQI) and HRQL using the Saint George's Respiratory Questionnaire. Additionally, lung function was assessed by spirometry, severity of dyspnea by the Modified Medical Research Council scale, and functional exercise capacity by the Six-Minute Walk Test. Twenty-one (70%) patients showed poor quality of sleep (PSQI > 5). HRQL was significantly correlated with quality of sleep (P = 0.02), post-bronchodilator FEV1 (P = 0.04), and severity of dyspnea (P < 0.01). Multiple regression analysis showed that quality of sleep was the best predictor of quality of life in our subjects. Our data suggest that quality of sleep is major determinant of HRQL in COPD. Increased efforts to diagnose and treat sleep problems, including measures to improve factors that adversely affect sleep should receive great attention in the daily management of these patients.