• The five-year ambulatory medical care experience of 400 patients with mental disorders was studied to test the "offset" hypothesis that patients receiving timely mental health speclallst treatment have lower subsequent utilization of, and charges for, care than patients not receiving such specialist treatment. Speciallst treatment was associated with significant offset savings in utilization and charges for the nonpsychiatric medical care of treated patients with either severe or less severe mental disorders. However, the visits and charges for such specialist treatment boosted the overall (nonpsychiatric plus mental health specialist) care utilization and charges of the specialist-treated patients above those of patients treated solely by their nonpsychiatric physicians; this overall increase was especially pronounced for patients with severe mental disorders. The findings suggest the need for randomized prospective offset studies comparing utilization, cost, and clinical outcomes.