Background: Many adolescents are referred to Child Protective Services for possible maltreatment every year, but not much is known about their organized and unstructured activity participation. Objective: The purposes of this study are to provide a description of organized and unstructured activity participation for adolescents who were possible victims of child maltreatment, and evaluate the demographic, family-related, and maltreatment-specific variables associated with participation. Method: Data came from 2776 youth ages 11-17 who participated in the National Study of Child and Adolescent Well-Being. Responses to the Youth Behavior Checklist from the Youth Self Report were grouped into five organized activities and seven unstructured activities. Descriptions of participation in activity types for the population were estimated using percentages. Logistic regression was used to test for associations of demographics and maltreatment experiences with participation. Results: Relatively low percentages of the population were engaged in organized activities (e.g., 13% in organized sports activities, 10% in mentored groups, and 6% in art and music organized activities), compared to unstructured activities (e.g., 91% in unstructured sports, 34% in games and hobbies, and 23% in computer games). Using English, attending school, having married caregivers, and living at home predicted more engagement in certain types of organized activities. Unstructured activity participation was mostly explained by demographic characteristics such as sex, age, and ethnicity. Conclusions: Future research should explore if increasing accessibility to existing school- or community-based organized activities improves well-being for adolescents at risk for maltreatment.