Very little is known about adult-onset offenders. This makes it difficult to know the most effective way for the criminal justice system to respond to these offenders. This project examined the nature of adult-onset offending in the 1983–84 Queensland Longitudinal Data Cohort and explored whether adult cautioning may be a suitable and cost-effective alternative to current court processing. Half of all offenders in this cohort started offending in adulthood (between 18 and 25 years), however, most adult-onset offenders had just one or two relatively less serious officially recorded offences. The authors argue that extending formal police cautioning to include first-time, less serious adult-onset offenders is a cost-effective strategy that would enable scarce criminal justice resources to be redirected to provide evidence-based interventions for more serious and prolific offenders who present an ongoing risk of offending.