Background: Health related quality of life (QoL) is severely impaired in COPD patients as a consequence of dyspnea and limited exercise tolerance, which lead to physical deconditioning and muscle atrophy resulting in weakness and fatigue. Psychosocial factors such as depression and anxiety also contribute to this impairment. Aim: To evaluate: a) the impact of COPD on quality of life, and b) the effect of 10 weeks of exercise training on exercise performance and on QoL. Patients and methods: The Spanish version of the Chronic Respiratory Questionnaire (CRQ) was applied to 55 COPD patients (FEV1 37 ± 13% pred) for the assessment of QoL and in 30 of them submitted to exercise training for 10 weeks. Exercise performance was evaluated by measuring: six-minute walking distance, maximal workload (Wmax), maximal O2 consumption (VO2max) as well as endurance time, blood lactic acid, dyspnea and leg fatigue during a submaximal exercise. Trained patients were evaluated before and after training. Results: COPD patients showed a reduction (mean ± SD) in the four domains of the CRQ: dyspnea (3.1 ± 0.9); fatigue (4.3 ± 1.3); mastery (4.65 ± 1.3), emotional function (4.1 ± 0.97), and in Wmax and VO2max (52 ± 16 Watt and 970 ± 301 ml/min). No significant relationship between the impairment in exercise tolerance and in QoL was observed. Exercise training significantly improved the four domains of QoL (p < 0.0001), Wmax (p < 0.05), VO2max (p < 0.02) and endurance time (p < 0.001). Isotime exercise measurements of dyspnea, leg fatigue and lactic acid decreased after training (p < 0.001, each). No significant relation between changes in QoL and changes in exercise performance were observed. Conclusions: Our results demonstrate that QoL is seriously impaired in patients with COPD and confirm: (a) the lack of relationship of QoL to the usually measured physiological parameters, and (b) the beneficial effect of exercise training on QoL through the reduction of symptoms. These findings stresses the need of measuring quality of life in our patients if we want to evaluate the impact of therapeutic procedures on well-being from the patients perspective. (Rev Méd Chile 2001; 129: 359-366)