The purpose of this study is to identify individual factors contributing to the perception of ethical behaviour of peers and whether or not the perception of ethical behaviour of peers is changing over time among undergraduate students. Participants were a convenience sample of 457 (n=457) undergraduate students from three geographically different US institutions. Data was collected in 2008 and in 2018. Multiple regression was used to see if there was a relationship between the years the data was collected on ethical behaviour of peers, the dependent variable. Ethical behaviour of self ([beta]=0.37, p<0.001), regulation of emotions ([beta]=-0.10, p<0.01), and the year data was collected ([beta]=0.14, p<0.001) were all found to be significant predictors of ethical behaviour of peers. Other factors not considered in the model, a more diverse sample, self-report methodology, and the interpretation of change in years are all potential limitations to this study. This study provides a longitudinal focus on ethical decision making.