Background: While the prevalence of language and communication difficulties among young people in custody is well established, holistic understanding of the complexity and co-occurrence of additional vulnerabilities among this population are rare. Methods: Ninety-three young people in a young offenders institution in England were assessed using the Comprehensive Health Assessment Tool, the Test of Word Knowledge, and a range of additional assessments of communication, cognition, and neurodevelopmental difficulties. Results: Forty-seven percent of the young people demonstrated an aspect of language skills significantly below the population average, with more than one in four identified as having impairment. Only one in four of those with an impairment had previously accessed speech and language services. Language needs were associated with difficulties with social communication and nonverbal cognition, as well as higher risk of self-harm and substance misuse. Conclusions: Earlier identification of language difficulties requires routine assessment of young people at risk of engagement in offending behavior. Where language difficulties are identified, holistic assessments of needs should be undertaken. There is a need for speech and language therapy provision within youth justice services, as well as in other services accessed by young people at risk of engagement in offending.