This report focuses on the implementation and evaluation of a 24-hour-a-day, in-home crisis inter vention, triage, and treatment service in a 110,000 member health maintenance organization. The in- home crisis intervention service averted the need for hospitalization in 80% of referred patients presenting for inpatient admission. A two-year analysis, involv ing more than 600 patients, found nearly four times fewer severe psychiatric relapses requiring readmis sion among patients triaged by the crisis intervention service, compared to patients hospitalized without going through its service. The service saved approx imately 3,347 days of hospital-based psychiatric care over the two-year study period. This program evalu ation data, combined with previous research, docu ments that for the vast majority of hospitalized psy chiatric patients, intensive in-home crisis interven tion and treatment services are a more effective and cost-efficient form of care.