Background: Patient safety education is an increasingly important component of the medical school curricula. Aims: This study reports on the development of a valid and reliable patient safety attitude measure targeted at medical students, which could be used to compare the effectiveness of different forms of patient safety education delivery. Methods: The Attitudes to Patient Safety Questionnaire (APSQ) was developed as a 45-item measure of attitudes towards five patient safety themes. In Study 1, factor analysis conducted on the responses of 420 medical students and tutors, revealed nine interpretable factors. The revised 37-item APSQ-II was then administered to 301 students and their tutors at two further medical schools. Results: Good stability of factor structure was revealed with reliability coefficients ranging from 0.64 to 0.82 for the nine factors. The questionnaire also demonstrated good criterion validity, being able to distinguish between tutors and students across a range of domains. Conclusions: This article reports on the first attempt to develop a valid and reliable measure of patient safety attitudes which can distinguish responses between different groups. The predictive validity of the measure is yet to be assessed. The APSQ could be used to measure patient safety attitudes in other healthcare contexts in addition to evaluating changes in undergraduate curricula.