Severe sexual sadism is a disorder of sexual preference that focuses on humiliation and subjugation of the victim, sometimes causing grievous injury or death. Sexual sadists pose a particular risk. However, the diagnosis as such is unreliable and prevalence estimates vary. In a sample of male high-security forensic inpatients who had committed sexual offenses, we found two-thirds of sexual sadists had not been identified as such prior to commitment. Possible reasons for missing the diagnosis are many fold. Present data support the notion that unrecognized sexual sadists more closely resembled non-sadistic sex offenders than accurately diagnosed sadists. In particular, initially unrecognized sexual sadists had less severe previous convictions, less vocational training, and experienced a less supportive upbringing than their correctly identified sadistic counterparts. The latter, in contrast, more often reached media coverage through their offense(s). We conclude that severe sexual sadism is likely an underdiagnosed, yet forensically highly relevant disorder.