The primary conclusion of the study is that severe sexual sadism is likely to be underdiagnosed yet forensically a highly relevant disorder when designing a treatment regimen. Out of the 535 patients, 240 were identified as sexual offenders. Based on diagnostic criteria for sexual sadism in DSM-IV-TR and ICD 10, these 240 sexual offenders could be further divided into 52 sexual sadists and 188 non-sadistic sexual offenders. DSM-IV-TR regards sexual sadism as a disorder of sexual preference (paraphilia) that ought to be diagnosed if the subject is repeatedly experiencing strong sexual urges, fantasies, or acts that include the infliction of psychological or physical suffering on others. These urges, fantasies, or acts must be present for at least half a year to the extent of impairing that individual’s functioning to a significant degree. Only one-third of the patients identified in this study as sexual sadists (n=52) had been diagnosed correctly prior to this study. Unrecognized sexual sadists more closely resembled non-sadistic sex offenders than accurately diagnosed sadists. Initially unrecognized sexual sadists had less severe previous convictions, less vocational training, and had experienced a less supportive upbringing than their correctly identified sadistic counterparts. The latter, in contrast, more often received media coverage of their offenses. All the patient charts were reviewed by experienced consultant forensic psychiatrists in order to determine whether they met the ICD 10 and DSM IV criteria for sexual sadism. Data were obtained on various other personal and clinical variables. 2 tables and 44 references