Although a considerable body of evidence has now accumulated about the link between psychotic illness and violent behaviour, fewer studies address this association in women. This data linkage study examined an entire population of female homicide offenders (N=55) in Victoria, Australia, over an eight-year period. Offence variables such as prior offending history and motivation for the offence were established by using police databases. The data were subsequently linked to a state-wide public mental health database and histories of prior mental health contact and relevant diagnoses, particularly psychosis, were obtained. Findings were compared to a comparison group from the general population. Of the 55 offenders, 11 (20%) had been diagnosed with a psychotic illness, nine prior to the offence and two after (nine (16%) with schizophrenia). The chance of finding psychosis among female homicide offenders was 20.77 times higher than among comparisons, while for schizophrenia the odds ratio was 43.17. Most of the mentally ill homicide offenders had a relatively long prior history of mental illness. The prevalence of known substance abuse did not differ for female homicide offenders with or without a psychotic illness but was higher than for controls.