The earliest characterisation of Australian sex offenders subjected to post-sentence legislation is presented. Demographic, developmental, clinical, and criminal characteristics were obtained for sex offenders under post-sentence orders in Western Australia, New South Wales, and Victoria. Data on 50 offenders were recorded from psychological and psychiatric risk assessment reports statutorily required at the initiation of post-sentence legal proceedings. The findings describe a group of demonstrably dangerous men who exhibited an early onset of sexual offending, high rates of mental disorder, sexual deviance, and antisociality. Their developmental histories are characterised by early deprivation, disadvantage, abuse, early exposure to substance abuse, and social and psychological dislocation. These offenders present a conundrum to criminal justice agencies. They are an objectively unfortunate group and have engaged in significantly harmful behaviours. However, the early onset of their offending suggests that early intervention services, such as those offered by mental health professionals, have a critically important role to play in any effort to alter offending trajectories such as those exhibited in this sample. A paradigm shift in public policy from a post hoc model to a well-resourced preventative and public health approach to the problem of sexual violence is proposed. Broad treatment implications are also considered.