Sexual sadism as described by the Diagnostic and Statistical Manual (DSM) of the American Psychiatric Association involves recurrent, intense sexually arousing fantasies, sexual urges, or behaviors involving real acts in which the psychological or physical suffering of the victim is sexually exciting to the person. However, this requires the diagnostician to infer sexual excitement generated by these features. The diagnostician attempts to determine whether or not a sexual offender meets criteria for sexual sadism based on inferences. This study examined aspects of the diagnoses of sexual sadism among incarcerated sexual offenders made by experienced forensic psychiatrists following DSM-III-R or DSM-IV criteria. The study attempted to examine limited aspects of the reliability and validity of the application of the diagnosis of sexual sadism within the practical operations of a forensic setting. The study consisted of archival psychiatric data extracted on 59 sexual offenders identified from 3 Canadian Federal penitentiaries. Four sets of data were extracted from the extensive files held in each prison including offense features, self-reported fantasies, phallometric assessment, and composite diagnoses score. The study revealed that the frequency with which the sexual offenders diagnosed as sadists displayed the features identified in the literature was far lower than had been previously observed. The sadists in this study did not differ from those deemed not to be sadists on numerous features; in addition the nonsadists actually displayed more of the putatively sadistic features than did those diagnosed as sadists. These results reflect very seriously on the adequacy of the diagnosis of sexual sadism as currently practiced in Correctional Service of Canada prisons. The results have relevance for the definition of sexual sadism and for its diagnosis. Tables and references