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International Classification of Diseases codes for child maltreatment can aid surveillance and research, but the extent to which they are used is not well established. We documented prevalence of the use of maltreatment-related codes, examined demographic characteristics of youth assigned these codes, and compared results with previous studies. Data were extracted from electronic health records of 0- to 21-year-olds assigned 1 of 15 maltreatment-related International Classification of Diseases, Ninth Revision, codes who had encounters in a large medical system over a 4-year period. Only 0.02% of approximately 2.5 million youth had a maltreatment-related code, replicating other studies. Results provide a dramatic contrast to much higher rates based on self-report or informant-report and referrals to Child Protective Services. Lack of documentation of maltreatment in electronic health records can lead to missed chances at early intervention, inadequate coordination of health care, insufficient allocation of resources to addressing problems related to maltreatment, and flawed public health data.