While procedural justice has been highlighted as a key strategy for promoting cooperation with police, little is known about this model’s applicability to subgroups engaged in illegal behaviour, such as illicit drug users. This study compares willingness to cooperate with police and belief in police legitimacy, procedural justice and law legitimacy among a population-based sample of Australian young adult amphetamine-type stimulant (ATS; i.e. ecstasy and methamphetamine) users and non-users. We then examine predictors of willingness to cooperate among ATS users. ATS users were significantly less willing to cooperate with police and had significantly lower perceptions of police legitimacy, procedural justice and law legitimacy, compared to non-users. However, belief in police legitimacy independently predicted willingness to cooperate among ATS users. We set out to discuss the implications of these findings for policing, including the role of procedural justice in helping police deliver harm reduction strategies.