Personal morality has long been considered a key predictor of criminal behaviour in criminological theory and research. However, cross-national comparative studies rarely assess the measurement invariance (MI) of morality constructs, which is often viewed as a prerequisite of direct international comparisons. The current study examines whether measures of personal morality, conceptualized as attitudes towards various rule-breaking behaviours, are comparable across three European samples of adolescents—the Peterborough Adolescent and Young Adult Development Study (PADS+) in the United Kingdom, the Malmö Individual and Neighbourhood Development Study (MINDS) in Sweden, and the Friendship and Violence in Adolescence study (FVA) in Germany—at ages 16 and 17. Using Bayesian approximate MI analyses, we test the comparability of morality dimensions across samples and over time. Results indicate that only some moral beliefs—specifically those pertaining to minor, school-based, and substance use infractions—achieve approximate MI, while beliefs regarding more severe (major) infractions do not. Consistent with theoretical expectations, lower morality generally correlates with greater crime involvement. However, this relationship is less uniform for the Swedish sample at age 17. Our findings have implications for cross-national comparisons of morality, as well as, more broadly, for the alignment of theoretical constructs and measurement practices and for international comparisons in criminological research.