Abstract: This article examines Australian legal responses to filicide in circumstances where mothers have killed their young children. We consider the potential legal defences that may be raised where postnatal depression (‘PND’) and other psychiatric disorders are present in cases of filicide: insanity/mental impairment, diminished responsibility/ substantial impairment by abnormality of mind, and infanticide. We then examine 28 cases of filicide, including both cases where PND evidence was adduced, and cases where PND evidence was not adduced but other mental health issues were considered. We look at the forensic use of and judicial responses to PND and other evidence of mental illness: how do medical practitioners and judicial officers present impairment of the defendant’s mental capacity? We also speculate on differences in sentencing outcomes and consider the policy and research implications of our findings.