Despite widespread agreement about the value of clinical trials, the proportion of patients who are enrolled in such trials is often considered to be too low. A comprehensive literature search was carried out for the period 1980 to the present, in order to review current data on barriers and facilitators to the development of multicentre clinical trials. Of 364 articles initially identified, 35 articles and 1 book were selected in order to assess the reasons that doctors and/or patients participate in clinical trials. This review emphasises the fact that doctors play a key role in the development and non-development of clinical trials. More studies, in particular studies outside the United States of America (USA), are needed in order better to understand doctors' attitudes towards clinical trials. Such studies should combine multivariate analyses and comparative approaches in order to associate doctors' behaviours with their individual characteristics, with the organisational context of their working environment and with the healthcare system.