We examined patterns and predictors of perceived need, use, and unmet need for mental health services by custodial grandchildren within the school-based and community-based delivery sectors. Data were from a national sample of 610 grandmothers caring for grandchildren ages 6 to 17 in the absence of biological parents. Overlapping use of services across both sectors was common, although use of school-based services (51%) was higher than that of community-based services (37%). Multiple regression analyses based on the Andersen Behavioral Model revealed the following shared predictors of mental health service use across both sectors: grandchildren’s externalizing symptoms, other grandchildren in the household with medical or psychiatric diagnoses, and corresponding use of services in the other sector. Predictors were similar when analyses were conducted with families recruited by either probability or convenience-based methods. Findings suggest the need to coordinate and integrate mental health services for custodial grandchildren across different delivery sectors.