Objectives: The aim of this study was to determine the prevalence of parental cognitive impairment in cases opened for child maltreatment investigation in Canada, and to examine the relationship between parental cognitive impairment and maltreatment investigation outcomes including substantiation, case disposition and court application. Methods: The method was secondary analysis of the Canadian Incidence Study of Child Abuse and Neglect (CIS-2003) core-data, which is derived from a multi-stage stratified cluster sample of 11,562 child maltreatment investigations. Results: Parental cognitive impairment was noted in 10.1% of sampled cases that were opened for child maltreatment investigation in 2003, and in 27.3% of sampled cases that resulted in child welfare court application. Neglect was the most common cause of concern. With child and case characteristics held constant, parental cognitive impairment predicted investigation outcomes. The data further suggest that the relationship between parental cognitive impairment and investigation outcomes was partially mediated by perceived parent non-cooperation, mental health issues and low social support. Conclusions: The number of children who are living with a parent with cognitive impairment and who are referred for protective services is thought to be increasing. Building systems capacity to support parents with cognitive impairment and promote child wellbeing is therefore essential to containing the human and economic costs of maltreatment and out-of-home care. Practice implications: A broad-spectrum approach is needed to support parents with cognitive impairment and their children. Equipping services with the knowledge, skills, and mandate they need to deliver evidence-based parent training is vital. However, strategies are also needed to tackle discrimination, alleviate family poverty, strengthen the social ties of parents with cognitive impairment and in turn, improve the life chances of their children. (Contains 4 tables and 6 figures.)