Although there has been significant interest among researchers in audit-quality-threatening behaviours (QTBs), the decision process through which staff auditors engage in those behaviours has received relatively little attention. It seems likely that the ethical intensity of the behaviours perceived by auditors may play an important role in that process; to date, this has not been tested. This study examines the mediating role of perceived ethical intensity in the relationship between perceived ethical culture of the firm and the auditors' ethical evaluation of, and intention to engage in, three different forms of QTBs. A multi-item measure of ethical intensity is developed and the findings provide the first empirical evidence of a direct relationship between perceived ethical intensity and ethical decision-making regarding QTBs. Moreover, the findings show that perceived ethical intensity fully mediates the relationship between perceived ethical culture and ethical decision-making. Implications of the findings for accounting firms and for researchers are discussed and areas for future research on the mediating role of perceived ethical intensity are suggested in the paper.