Within the field of criminology, the Situational Action Theory has gained increased attention. It is a theory aiming to explain moral rule breaking in general, and criminal acts in particular, through the interaction between an individual and the immediate environment in which she finds herself. This interaction initiates a perception-choice process. According to the theory, what inhibit or enable us to see crimes as action alternatives is our sense of what is right or wrong to do in certain situations – our morality. Given the theoretical importance placed on morality in the explanation of crime, this work aims to study matters of moral development. Analyses are based on a longitudinal sample of individuals moving through adolescence; an important period in life considering changes occurring at the time. As the adolescents’ autonomy tends to grow, so does the impact of peers. More specifically, the aim is to study interindividual differences in intraindividual change by looking closer at the relationship between changes in delinquent peer association and criminogenic exposure on the one hand, and changes in morality on the other. This is done through a series of linear growth models. The sample is derived from the Swedish longitudinal project Malmö Individual and Neighbourhood Development Study (MINDS), and is comprised of 386 adolescents participating in three waves of data collection (at ages 15-16, 16-17, and 18-19). Results indicate that morality by and large decreases over time, and that this decrease is homogenous for the sample (i.e. no significant variance). Neither is there any significant correlation between initial level of morality and subsequent change. Results also indicate that a higher initial level of morality is significantly associated with a higher increase of delinquency amongst peers over time (but that higher initial levels of delinquent peer association is not significantly associated with subsequent change in morality). Furthermore, an increasing rate of delinquency amongst the adolescents’ peers over time is associated with a decreasing rate of morality, and a decreasing rate of criminogenic exposure is associated with a decreasing rate of morality. This moral change is to be discussed within a methodological and criminological framework.