This paper reports on an application of discrete choice modelling to the measurement of patient preferences over asthma symptoms. A sample of patients with moderate to severe asthma was asked to choose between a series of pairs of scenarios characterised by different combinations of asthma symptoms. Their responses were analysed using a random effects ordered probit model. The results implied that patients weighted some symptoms more highly than others. Discrete choice modelling proved to be a useful approach for developing preference based outcome measures, although the results show how, in contexts where preferences over health care outcomes based on symptoms or some measure of health status are involved, a conventional linear additive model may not always be suitable.