Background: According to the Declaration of Helsinki, patients who take part in a clinical trial must be adequately informed about the trial's aims, methods, expected benefits, and potential risks. The declaration does not, however, elaborate on what “adequately informed” might amount to, in practice. Medical researchers and Local Research Ethics Committees attempt to ensure that the information which potential participants are given is pitched at an appropriate level, but few studies have considered whether the patients who take part in such (...) trials feel they have been given adequate information, or whether they feel able to understand that information.Objectives: To explore trial participants' views on the amount of information provided, and of their own understanding of that information.Design: Structured interviews of patients participating in clinical trials for the treatment of chronic medical condition.Findings: Patients generally felt they were given an appropriate amount of information, and that they were able to understand all or most of it. They felt they were given adequate time to ask questions before agreeing to take part. In comparison with treatment given outwith the research setting, patients generally felt they received more information when participating in a clinical trial.Conclusions: Researchers sometimes complain that patients are given too much information during clinical trials, and have limited understanding of that information. The present study shows that this perception is not necessarily shared by patients. More research is needed in this area, particularly to gauge whether patient understanding is indeed accurate. (shrink)