Chronic obstructive pulmonary disease (COPD) is a major cause of morbidity in old age. It leads to reduced quality of life (QoL), but the factors that contribute to this are less understood. There is no consensus on measurement of QoL in elderly COPD patients. We assessed (a) factors predicting QoL in elderly COPD out-patients and (b) specificity (SP), sensitivity (SEN), positive and negative predictive values (PPV and NPV) and repeatability of two disease-specific QoL instruments, the Chronic Respiratory Disease Questionnaire (CRQ) and the Breathing Problems Questionnaire (BPQ) in elderly people. All subjects also completed an ADL measure [Nottingham Extended ADL (NEADL)] and a measure of psychological well-being [Brief Assessment of Depression Cards (BASDEC)] as well as a 6-min walk test. Subjects comprised 96 (56 men) elderly out-patients with irreversible COPD aged 70-93 years (mean 78) who were clinically stable for > or = 6 weeks. Controls were 55 (23 men) aged 71-90 years (mean 78) with normal lung function. All were cognitively intact. Mean FEV1/FVC in COPD subjects was 45.5 (SE = 1.4)% and for controls was 71.4 (SE = 1.3)%. Repeatability was good for both BPQ and CRQ with no significant difference. There were no significant differences in specificity and positive predictive values between the two questionnaires but BPQ performed better than CRQ with regard to sensitivity (P = 0.02) and NPV (P < 0.001). A multiple regression analysis was used to identify variables that best predicted BPQ and CRQ in COPD subjects. For BPQ predictive values were NEADL (P < 0.0001); BASDEC (P < 0.0001); age (P < 0.0001); 6-min walk distance (P = 0.001); body mass index (P < 0.05); resting oxygen saturation (P < 0.05); and household composition (living alone or with relatives, P = 0.05). In contrast only the following predicted CRQ: NEADL, BASDEC and resting oxygen saturation. Sixteen per cent of the variance in BPQ was accounted for by NEADL score, 9% by BASDEC, 4% by age and 3% by 6-min walk distance (total r2 = 0.70). It was concluded that: (1) BPQ provides more valid assessment than CRQ of QoL in elderly COPD subjects; (2) severity of disease in terms of its impact on QoL is not predicted by lung function tests; (3) the most important determinants of QoL are ADL score and emotional status.