ABSTRACT: BACKGROUND:Youth mental health interventions aimed at reducing substance use and delinquency in adolescents compete with other types of interventions for reimbursement from public funding. Within the youth mental health domain, delinquent acts impose high costs on society. These costs should be included in economic evaluations conducted from a societal perspective. Although the relevance of these costs is recognized, they are often left out because the unit costs of delinquent acts are unknown. AIMS OF THE STUDY:This study aims to provide a method for estimating the unit costs per perpetrator of 14 delinquent acts common in the Netherlands and included in self reported delinquency questionnaires: robbery/theft with violence, simple theft/pickpocketing, receiving stolen goods, destruction/vandalism of private or public property, disorderly conduct/discrimination, arson, cybercrime, simple and aggravated assault, threat, forced sexual contact, unauthorised driving, driving under the influence, dealing in soft drugs, and dealing in hard drugs. METHODS:Information on government expenditures and the incidence of crimes, number of perpetrators, and the percentage of solved and reported crimes was obtained from the national database on crime and justice of the Research and Documentation Centre of the Ministry of Justice and Security, Statistics Netherlands, and the Council for the Judiciary in the Netherlands. We applied a top-down micro costing approach to calculate the point estimate of the unit costs for each of the delinquent acts and, subsequently, estimated the mean (SD) unit costs for each of the delinquent acts by taking random draws from a triangular distribution while taking into account a 10% uncertainty associated with the associated point estimate. RESULTS:The mean (SD) unit costs per delinquent act per perpetrator ranged between EUR495 (EUR1.30) for "Driving under the influence" and EUR33,813 (EUR78.30) for a "Cybercrime". These unit costs may be considered as outliers as most unit costs ranged between EUR 2,600 and EUR 13,500 per delinquent act per perpetrator. DISCUSSION:This study is the first to estimate the unit costs per delinquent act per perpetrator in the Netherlands. The results of this study enable the inclusion of government expenditures associated with crime and justice in economic evaluations conducted from a societal perspective. IMPLICATIONS FOR HEALTH CARE PROVISION AND USE:Youth mental health interventions aimed at reducing substance use and delinquency in adolescents are increasingly subjected to economic evaluations. These evaluations are used to inform decisions concerning the allocation of scarce healthcare resources and should cover all the costs and benefits for society, including those associated with delinquent acts. IMPLICATIONS FOR HEALTH POLICIES:The results of this study facilitate economic evaluations of youth mental health interventions aimed at reducing substance use and delinquency in adolescents, conducted from a societal perspective. IMPLICATIONS FOR FURTHER RESEARCH:Based on health-economic evaluations conducted in the field of youth mental health and the results of the current study, we recommend including the estimated unit costs in guidelines for health-economic evaluations conducted from a societal perspective. Future research could aim at examining whether these unit costs require regular updating. The methodology applied in this study allows for this.