Background Information on psychopathological characteristics of sexual homicide offenders is scarce. Aims To investigate criminal, paraphilic and personality trait differences between serial and single‐victim sexual homicide offenders. Methods All 73 single‐victim and 13 serial sexual homicide offenders presenting within a cohort of 671 men sentenced for sexual crimes between 1994 and 2005 and serving their sentence in one high‐security Canadian prison and who consented to interview were assessed and compared on their offending patterns, personality pathology and paraphilic behaviours. Results Serial sexual homicide offenders were more likely than the single offenders to report deviant sexual fantasies, having selected victims with distinctive characteristics, to have targeted strangers, structured premeditation and/or verbal humiliation of their victims during the offences. Personality pathology, defined by at least two Diagnostic and Statistical Manual of Mental Disorders IV criteria for personality disorder, was common in both groups, but the serial offenders were more likely to have narcissistic, schizoid and/or obsessive–compulsive traits; they were also more likely to engage in sexual masochism, partialism, homosexual paedophilia, exhibitionism and/or voyeurism. Implications for practice Samples of serial sexual homicide offenders will, fortunately, always be small, and it may be that more could be learned to assist in preventing such crimes if data from several studies or centres were pooled. Our findings suggest that an investigation of sexual homicide offenders should include strategies for evaluating premeditation as well as personality and paraphilic characteristics. Crime scene features that should alert investigators should include similar characteristics between victims and particular aspects of body exposure or organisation. Copyright © 2014 John Wiley & Sons, Ltd.