OBJECTIVES: We report the first survey on French physicians and patients participating to assess motivations prior enrolment and benefits and constraints perceived after participation. METHOD: Twenty physicians were interviewed and 37 patients completed a questionnaire during clinical study participation. RESULTS: If the main patient's motivation is altruistic, physician wish their own patient feel better. After participation, patient is satisfied with being part of a research effort and contributing to medical science. Effect of trial treatment on physical well-being seems less pronounced. Main constraint is the randomisation to placebo group. For physicians, the main benefit is getting research experience and training. Main constraints are logistical. Otherwise, perceptions on the same clinical trial depend on participant. In fact, physician usually overestimates constraints of clinical trial for patient. CONCLUSION: The knowledge of patients and physicians perceptions of clinical trials and its taking into account should probably reduce difficulties in the recruitment in France.