Sex offending can be comprehended as a constellation of acts of a sexual nature against an individual without that individual’s consent (Hale et al., 2005) and can take many forms, from offensive exposure to the possession of illegal material (Thomas, 2001). It is thus an interpersonal crime, whereby the relationship between the perpetrator and the victim is the key to fully understand the crime. The aim of this article is to gather the evidence-based studies in the field and consequently to propose an inpatient sex offender treatment programme, with particular focus on the assessment tools and treatment approach to be implemented. Lastly, a service evaluation protocol using appropriate clinical and service outcome measures will be established.