The authors sought to determine whether a mobile crisis intervention service can effect cost savings by diverting patients from hospital admission into community-based treatment. They followed 50 consenting adult psychiatric patients for 6 months from the first day they were seen by the crisis intervention service. At the first visit, the crisis team obtained data to assess each patient's degree of risk for hospitalization. Investigators then kept a day-by-day record of every psychiatric treatment received by each patient, in an effort to determine the cost effectiveness of crisis intervention. The authors present evidence that crisis intervention permits some patients who would otherwise have been hospitalized to remain in the community and that savings thus realized exceed the expense of crisis intervention.