This study assessed the impact of the Integrated Care Program (ICP), a new Medicaid managed care model in Illinois, on health services utilization and costs for adults with behavioral health conditions. Data sources included Medicaid claims, encounter records, and state payment data for 28,127 persons with a behavioral health diagnosis. Difference-in-differences models, in conjunction with propensity score weighting, were used to compare utilization and costs between ICP enrollees and a fee-for-service (FFS) comparison group. The model considered the impact of the SMART Act, which restricted access to care for the comparison group. Before the SMART Act, ICP was associated with 2.8 fewer all-cause primary care visits, 34.6 fewer behavioral health-specific outpatient visits, and 2.5 fewer all-cause inpatient admissions per 100 persons per month, and $228 lower total costs per member per month relative to the FFS group. After the SMART Act, ICP enrollees had increased outpatient and dental services utilization without significantly higher costs. The relative increase in utilization was due primarily to decreased utilization in the restricted FFS group after the SMART Act. By the end of the study period, the ICP group had 13.3 more all-cause primary care visits, 1.5 more emergency department visits, and 1.4 more dental visits per 100 persons per month relative to the FFS program. A fully-capitated, integrated managed care program has the potential to reduce overall Medicaid costs for people with behavioral health conditions without negative effects on service utilization.