Individuals who engage in sexual offenses may be afflicted with a paraphilic disorder or sexual deviation syndrome. Paraphilias are psychiatric disorders characterized by deviant and culturally non-sanctioned sexual fantasies, thoughts, and/or behaviors. A proportion of these individuals may also suffer from symptoms of mental illness that can go unrecognized. Although the etiology and pathophysiology of paraphilic disorders continue to be under investigation, data from empirical, biomedical, and psychopharmacological studies suggest abnormalities at a biological level. This article will discuss and review clinical and neurobiological characteristics of the paraphilias. To this end, we will begin with a general exploration and overview of basic principles that are germane to the subject matter and will conclude with an examination of the most recent relevant research findings. (Contains 4 tables.)