This study aimed to examine the nature and extent of use of the social networking service Facebook by young medical graduates, and their utilisation of privacy options. We carried out a cross-sectional survey of the use of Facebook by recent medical graduates, accessing material potentially available to a wider public. Data were then categorised and analysed. Survey subjects were 338 doctors who had graduated from the University of Otago in 2006 and 2007 and were registered with the Medical Council of New Zealand. Main outcome measures were Facebook membership, utilisation of privacy options, and the nature and extent of the material revealed. A total of 220 (65%) graduates had Facebook accounts; 138 (63%) of these had activated their privacy options, restricting their information to 'Friends'. Of the remaining 82 accounts that were more publicly available, 30 (37%) revealed users' sexual orientation, 13 (16%) revealed their religious views, 35 (43%) indicated their relationship status, 38 (46%) showed photographs of the users drinking alcohol, eight (10%) showed images of the users intoxicated and 37 (45%) showed photographs of the users engaged in healthy behaviours. A total of 54 (66%) members had used their accounts within the last week, indicating active use. Young doctors are active members of Facebook. A quarter of the doctors in our survey sample did not use the privacy options, rendering the information they revealed readily available to a wider public. This information, although it included some healthy behaviours, also revealed personal information that might cause distress to patients or alter the professional boundary between patient and practitioner, as well as information that could bring the profession into disrepute (e.g. belonging to groups like 'Perverts united'). Educators and regulators need to consider how best to advise students and doctors on societal changes in the concepts of what is public and what is private.