In this paper we will test one of the key assumptions of Situational Action Theory: that individuals’ (law-relevant) morality is more fundamental to their crime involvement than their ability to exercise self-control. We specifically hypothesize that, for individuals with a strong morality, their capability to exercise self-control plays less of a role in their crime involvement than it does for individuals with a weak morality, whose capability to exercise self-control may substantially influence their engagement in crime. To test this hypothesis we use data from the Peterborough Youth Study (PYS), a cross-sectional survey of 1957 adolescents aged 14—15 from the UK city of Peterborough. The findings support the main hypothesis: young people with a strong (law-relevant) morality do not engage in crime, regardless of their ability to exercise self-control. However, among those with a weaker (law-relevant) morality, their ability to exercise self-control is an important factor in their crime involvement.