Background The intergenerational risk for mental illness is well established within diagnostic categories, but the risk is unlikely to respect diagnostic boundaries and may be reflected more broadly in early life vulnerabilities. We aimed to establish patterns of association between externalising and internalising vulnerabilities in early childhood and parental mental disorder across the full spectrum of diagnoses.Methods A cohort of Australian children (n = 69 116) entering the first year of school in 2009 were assessed using the Australian Early Development Census, providing measures of externalising and internalising vulnerability. Parental psychiatric diagnostic status was determined utilising record-linkage to administrative health datasets.Results Parental mental illness, across diagnostic categories, was associated with all child externalising and internalising domains of vulnerability. There was little evidence to support interaction by parental or offspring sex.Conclusions These findings have important implications for informing early identification and intervention strategies in high-risk offspring and for research into the causes of mental illness. There may be benefits to focusing less on diagnostic categories in both cases.