The effects of intervention can be evaluated in different ways, and objective measurements of changes in lung function are commonly used as the outcome measure. Patient-reported outcome (PRO) is an umbrella term used for all patient-based assessment. One important PRO is health-related quality of life (HRQL), which may be used an an evaluative or discriminative measure. The research showed that completion up to five PRO questionnaires was well accepted by subjects with COPD. HRQL questionnaires might be used for evaluative purposes. HRQL questionnaires appear to have a possibility to be used for discriminative purposes in COPD and asthma, and for comparison of the diseases. Symptoms correlated with HRQL, whereas between lung function and HRQL, the relationship was weaker. HRQL seems to deteriorate with disease severity in COPD and asthma, as measured by lung function, or with age. However, a great variation was noticed.