Objective: To examine whether and to what extent specific chronic health conditions place young children at risk of maltreatment. Methods: The study used a sample of Illinois children (born between January 1990 and March 1996) who were through age 3 continuously enrolled in Medicaid, a public health insurance program for low-income families. The study used "paid claims" data and ICD-9-CM health codes to identify children with one or more of three chronic conditions: chronic physical illness, developmental delay/mental retardation (dd/mr), and behavior/mental health conditions (b/mh). The analysis used Cox proportional hazard models to estimate the risk of substantiated child maltreatment that each of these health conditions confer on children under age 6. Results: Among children under age 6, 24.1% had chronic physical health conditions, 6.1% had b/mh conditions, and 4.2% had dd/mr. Among the children, 11.7% were maltreated (abused or neglected). Children with b/mh conditions were 1.95 times more likely than children without such conditions to be victims of child abuse or neglect. Children with chronic physical health conditions were 1.1 time more likely to be maltreated (p less than or equal to 0.001). In contrast, children with dd/mr were not at an increased risk of maltreatment. Further, if the child had a prior history of abuse or neglect before age 3 and was also diagnosed with a behavioral health condition, that child was 10 times more likely to be maltreated again (relative risk of 9.2, p less than or equal to 0.0001). Conclusions: Behavioral/mental health conditions placed low-income children under age 6 at the highest risk of abuse or neglect. Developmental delay/mental retardation, however, did not appear to increase the risk of maltreatment, while chronic physical health conditions increased the risk slightly among this group of children. Therefore, identified behavior/mental health in young, low-income children should be considered a risk factor for potential abuse to pediatricians and other health professionals. Child protection agencies should be trained to identify behavioral/mental health conditions of children. Practice implications: Chronic behavioral/mental health conditions place young children at heightened risk of abuse or neglect. Early detection of mental or psychosocial health conditions is mandated by the Individuals with Disabilities Education Act (IDEA), a federal law that governs how state and public agencies provide services to children with disabilities. Given the higher risk of abuse and neglect among children with behavioral/mental health conditions, clinicians should give added scrutiny to these children. Child protection agencies should also be trained to identify behavioral/mental health conditions, and more states should record disability status in their abuse records. (Contains 4 tables.)