OBJECTIVES: To examine the association between child maltreatment (abuse and neglect) in one sibling and that in another as well as associated risk factors. METHODS: The participants were 520 sibling pairs enrolled in a population-based birth cohort study in Brisbane, Australia (N = 1040). Exposure to suspected child maltreatment was measured by linkage with state child protection agency data. Self-reports of childhood sexual abuse were also collected at the 21-year follow-up. RESULTS: There were notifications in both children for 8.5% of the sibling pairs (n = 44). A notification in the first sibling was associated with a 60-fold increase in the likelihood of a notification in the second sibling (95% confidence interval: 29.3-125.1), resulting in nearly three-quarters being the subject of a report. In terms of the subtypes, neglect revealed the strongest association, followed by sexual abuse. At the 21-year follow-up, 58% of second siblings reported sexual abuse when the first sibling disclosed similar experiences. On adjusted analyses, maternal age of ,20 years was the strongest and most consistent predictor of abuse, with indigenous status, maternal depression, parental relationship, and familial poverty playing a lesser role. CONCLUSIONS: Our results highlight the close association between child abuse in one sibling and maltreatment in a second sibling as well as possible risk factors. Greater awareness of these factors may inform interventions, particularly primary and secondary prevention.