Background: Individuals with speech, language and communication needs (SLCN) are at greater risk of contact with the criminal justice system. Diagnosis and appropriate treatment of SLCN reduces these risks, leading to better life outcomes for the individual as well as broader social and economic benefits. These youth represent a particularly high-priority group for research into language deficits, as the juvenile justice system involves situations with a high risk or serious consequences that rely upon the application of effective language skills. Whilst some studies have established some gains in speech and communication from speech pathology (SP) interventions during custody, there is limited evidence on the long-term impact of these gains following release from custody. Similarly, few studies have directly measured the cost savings associated with early SP on subsequent youth antisocial behaviour and crime. Aims: To estimate the youth antisocial behaviours, youth justice (YJ) contacts and associated costs (from a justice perspective) of childhood SLCN. Methods & Procedures: Using 12 years of data from a longitudinal study of Australian children and young people, we employ a panel fixed-effects model to explore the relationship between SLCN and youth antisocial behaviour and youth offending between 12 and 17 years of age. Using these results, we estimate the cost of SLCN and subsequent cost savings associated with identification of SLCN. Outcomes & Results: The results showed that the annual cost of SLCN to the YJ system (exchange rate as at 9 December 2020) is A$875 (95% confidence interval (CI) = A$195, A$1916) (US$$649, €536, £485) per person who participates in youth crime, which is due to higher rates of youth antisocial behaviour and youth offending. Identification of SLCN (defined by SP treatment) appears to have a positive impact on youth antisocial behaviour and crime, mediated through improved language and communication. On average, young people with a history of 'identified' SLCN incur A$188 (95% CI = A$42, A$412) lower YJ costs (US$$140, €105, £115), compared with the same individual, before identification. Over the lifetime of the individual, this equates to A$9.2 million (95% CI = A$2.05 million, A$20.2 million) (US$$6.8 million, €5.6 million, £5.1 million) cost savings to the YJ system (A$3389 per person with SLCN) (2020 Australian dollars) (US$2513, €2074, £1880). Conclusions & Implications: Overall, the findings revealed that young people with SLCN have an elevated risk of youth antisocial behaviour and crime. However, the identification of SLCN (and subsequent treatment) leads to changes in the offending risk trajectory for these individuals, resulting in lower rates of youth antisocial behaviour and consequently lower rates of crime and its associated justice costs.