Objectives To investigate risk perception relating to living kidney donation, to compare the risk donors would accept with current practice and identify influential factors. Design An observational study consisting of questionnaires completed by previous living donors and the general public. Participants selected the risk they would accept from a list of options, in various scenarios. Risk communication was investigated by randomly dividing the sample and presenting risk differently. Setting Primary care (two centres) and secondary care (one centre), London. Participants 175 questionnaires were sent to patients who had previously undergone living-donor nephrectomy and to members of the public consulting a general practitioner. The living-donor sample comprised 77 consecutive donors at Guy's Hospital from May 2003 to January 2005. The general-public sample was recruited from two London healthcare centres. Of the eventual 151 participants, 61 were living donors and 90 were from the general public. Main outcome measure The amount of risk a participant would accept to donate a kidney. Results 74% of participants were willing to accept a risk of death higher than 1/3000. The most commonly accepted risk was 1/2 (29%). Those presented with a 'chance of survival' accepted higher risks than those presented with a 'risk of death' (p<0.01). Greater risks were accepted when the recipient was closely related and, for some, when the recipient's prognosis was worse. No difference was observed between the living-donor and general-public groups. Conclusions Kidney donors will accept a higher risk of death than is currently quoted, especially if risks are presented in terms of chance of survival.