OBJECTIVES: To compare attitudes of medical and law students toward informing a cancer patient about diagnosis and prognosis and to examine whether differences are related to different convictions about benefit or harm of information. Setting and design: Anonymous questionnaires were distributed to convenience samples of students at the University of Geneva containing four vignettes describing a cancer patient who wishes, or alternatively, who does not wish to be told the truth. PARTICIPANTS: One hundred and twenty seven medical students and 168 law students. MAIN OUTCOME MEASURES: Five point Likert scale of responses to the vignettes ranging from "certainly inform" to "certainly not inform" the patient. RESULTS: All medical students and 96% of law students favoured information about the diagnosis of cancer if the patient requests it. Seventy four per cent of medical students and 82% of law students favoured informing a cancer patient about his or her prognosis (p = 0.0003). Thirty five per cent of law students and 11.7% of medical students favoured telling about the diagnosis (p = 0.0004) and 25.6% of law students and 7% of medical students favoured telling about the prognosis (p < 0.0001) even if the patient had clearly expressed his wish not to be informed. Law students indicated significantly more often than medical students reasons to do with the patient's good, legal obligations, and the physician's obligation to tell the truth, and significantly less often than medical students that their attitude had been determined predominantly by respect for the autonomous choice of the patient. CONCLUSION: Differences in attitudes according to the type of case and the type of studies were related to convictions about the benefit or harm to the patient caused by being given information. The self reported reasons of future physicians and future lawyers are helpful when considering means to achieve a better acceptance of patients' right to know and not to know.