In explaining public willingness to cooperate with the police, researchers have disproportionally emphasised legitimacy. Deterrence is presumed to be irrelevant; where it is considered, the approach appears perfunctory. Using survey data from 530 young adults in Ghana, this study examines the relative importance of deterrence and legitimacy perceptions in shaping willingness to report corruption transactions to the police. The results show that perceptions of legitimacy do not affect the young adults’ willingness to report corruption to the police. The most important and consistent predictors of willingness to report corruption to the police are deterrence-based; perceptions, specifically, of the certainty of being apprehended for engaging in corrupt transactions, of the severity of sanctions against such transactions, and of the cooperative intentions of other citizens. Deterrence proved particularly salient among those who claimed ignorance of where to report corrupt transactions.