Individuals who stalk strangers and acquaintances are under-studied, although there is some evidence suggesting a greater prevalence of psychopathology than is present in those who stalk former partners. This study investigated the nature and prevalence of psychopathology in a sample of stranger and acquaintance stalkers and whether psychopathology was associated with increased duration or serial stalking in this group. It was hypothesised that mental illness, and specifically psychosis, would be more prevalent among strangers and acquaintances than among ex-intimate stalkers. Method: Two hundred and eleven stalkers (10 female; mean age = 35, SD = 10.8; 71 ex-intimates) were recruited between 2002 and 2007 from a specialist service in Melbourne, Australia. Each underwent psychiatric and psychological assessment and disorders were diagnosed according to DMS-IV-TR criteria. Non-parametric independent sample tests were used to examine associations between relationship type and psychopathology, and to identify individual and stalking-related characteristics associated with increased duration and serial stalking.