Background: Despite considerable health consequences of child abuse and neglect, there is limited evidence on hospitalizations in this population. Objectives: To describe frequency and reasons for hospitalization by lifetime child protection system (CPS) involvement. Participants: 608,540 children born from January 1, 1986 to June 30, 2017 in South Australia, Australia Methods: Using linked administrative data on CPS involvement and hospitalizations, we descriptively examined cumulative incidence, cumulative count and reasons for hospitalization from infancy to early adulthood by CPS involvement. Results: By 16.5 years of age, cumulative incidence of ever-being hospitalized was 58% (95% CI 58-58) for children with no CPS involvement and significantly higher (72% (95% CI 71-73) to 88% (95% CI 86-90), P < 0.001) among those with different levels of CPS involvement. Cumulative mean counts of hospitalizations were highest at every age for those placed in out-of-home-care (reaching 7.7 by 16.5 years), almost four times higher than for children with no CPS involvement (2.0 by 16.5 years). Most frequent reasons for hospitalizations were similar across CPS involvement in the early years. From adolescence through early adulthood, mental health, and ‘injury, poisoning or toxic effects of drugs’ were frequent reasons for hospitalization among individuals with CPS involvement. Conclusions: This study highlights the vulnerability of children who have been maltreated, or are at risk of maltreatment, and the urgency of implementing effective preventive strategies early in life including consideration of adequate responses of child protection services. Frequent hospitalizations for mental health and injury confirms the potentially preventable nature of these hospitalizations.