Candidates taking multiple choice question (MCQ) examinations are often unsure of the best strategy to use when uncertain of the answer to a question. Some authorities advocate a cautious ‘never guess' strategy and others suggest a bold ‘guess everything’ approach. In this study, candidates who had taken a MCQ paper were asked to go back and guess the questions initially marked ‘don't know’. The resultant ‘guess scores' ranged from −0.6% to 6%. It was concluded that many candidates could substantially increase their scores by adopting a bolder approach. It is proposed that the guess score is a useful measure of the effectiveness of the candidate's MCQ technique.