Purpose We examined whether medical students’ opinions on the acceptability of a behaviour were influenced by previously encountering a similar professionally challenging situation, assessed the magnitude of effect of ‘experience’ compared to other demographic factors which influence medical students’ opinions, and evaluated whether opinions regarding some situations/behaviours were more susceptible to ‘experience’ bias? Methods Confidential, on-line survey for medical students distributed to Australian and New Zealand (AUS/NZ) medical schools. Students submitted de-identified demographic information, provided opinions on the acceptability of a wide range of student behaviours in professionally challenging situations, and whether they had encountered similar situations. Results 3171 students participated from all 21 Aus/NZ medical schools (16% of registered students). Medical students reported encountering many of the professionally challenging situations, with varying opinions on what was acceptable behaviour. The most significant factor influencing acceptability towards a behaviour was whether the student reported encountering a similar situation. The professional dilemmas most significantly influenced by previous experience typically related to behaviours that students could witness in clinical environments, and often involved breaches of trust. Conclusions Our results demonstrate the relationship between experience and medical students’ opinions on professional behaviour- the ‘Schweitzer effect’. When students encounter poor examples of professional behaviour, especially concerning trust breaches, it significantly influences their perception of the behaviour. These results highlight the importance of placing students in healthcare settings with positive professional role modelling/work cultures.