We examined patterns and predictors of the perceived need, use, and unmet need for mental health services by custodial grandchildren within both the school-based and community-based delivery sectors. Data were self-reported by a national sample of 610 custodial grandmothers providing full-time care to grandchildren ages 6 to 17 in the absence of biological parents. Although overlapping use of services across both sectors was common, the overall use of school-based services (51%) was higher than that of community-based services (37%). Using theAndersen Social and Behavioral Model (1995) the following shared predictors of mental health service use across both sectors by custodial grand-families emerged: grandchildren’s externalizing symptoms, having other grandchildren in the household with medical or psychiatric diagnoses and corresponding use of services in the other sector. Predictors were largely the same regardless of whether analyses were conducted with families recruited by probability or convenience based sampling methods. Findings suggest the necessity to coordinate and integrate the availability and implementation of mental health services for custodial grandchildren across different delivery sectors.