Chronic obstructive pulmonary disease (COPD) is an increasing public health problem, generating considerable costs. The objective of this study was to identify factors affecting COPD-related costs. A cohort of 179 subjects with COPD was interviewed over the telephone on four occasions about their annual use of COPD-related resources. The data set and explanatory variables were analysed by means of multivariate regression techniques for six different types of cost: societal (or total), direct (health care) and indirect (productivity), and three subcomponents of direct costs-hospitalisation, outpatient and medication. Poor lung function, dyspnoea and asthma were independently associated with higher costs. Poor lung function (severity of COPD) significantly increased all six examined cost types. Dyspnoea (breathing problems) also increased costs, though to a varying extent. The presence of reported asthma increased total, direct, outpatient and medication costs. Poor lung function and, to a lesser extent, extent of dyspnoea and concomitant asthma, were all strongly associated with higher COPD-related costs. Strong efforts should be made to prevent the progression of COPD and its symptoms.