The assessment of sexual aggression presents many difficulties for clinicians. The tendency of offenders to minimise or deny their offending, and their frequent distrust of mental health professionals, require high levels of skill to circumvent. In addition, the multifactorial nature of rape means that assessment needs to cover a broad range of content areas and utilise a number of different methods. In this paper we suggest that a comprehensive assessment should inquire into the developmental history of rapists, social competency, attitudes and beliefs about women and sexual crimes, sexual knowledge, sexual preferences and disorders, empathy, offence variables, psychiatric history, and substance abuse. The clinical interview remains the primary method of information acquisition, and needs to be tailored to match the particular interpersonal style of rapists. The use of psychometric and physiological measures are also valuable sources of clinical data.