This study examines the initial effects of the Massachusetts Mental Health and Substance Abuse Program on 24-hour care for children and adolescents. Analysis of Medicaid claims shows that under managed care, access to 24-hour services, the number of service users, and admissions increased, while length of stay and expenditures decreased. The decomposition of the savings indicated that although the increase in admissions would have added an additional $2.7 million to expenditures without managed care, the carve-out saved $9.1 million in the first year through changes in length of stay, service settings, and price per day. The managed care variable was not significant in the regression models examining rapid readmission.