This study examined whether Medicaid claims and other administrative data could identify high-need individuals with serious mental illness in need of outreach in a large urban setting. A claims-based notification algorithm identified individuals belonging to high-need cohorts who may not be receiving needed services. Reviewers contacted providers who previously served the individuals to confirm whether they were in need of outreach. Over 10,000 individuals set a notification flag over 12-months. Disengagement was confirmed in 55 % of completed reviews, but outreach was initiated for only 30 %. Disengagement and outreach status varied by high-need cohort.