Many postgraduate students in Britain experience a 'mock' viva some time before their 'real' one, but little has been published on this aspect of gaining a Ph.D. or professional doctorate. In this study questionnaire data on the experiences and feelings of 29 UK postgraduate students concerning their mock vivas are summarized. The results suggest that there are considerable disparities in procedures within and across institutions, and that students are frequently asked different questions in the mock and the real viva. Nonetheless, these mock vivas were judged to be helpful by 26 (90%) of the students concerned. The implications of these findings for institutions, departments and doctoral students are discussed.