Objective: To evaluate a methodology of managing high cost patients, called Case Management Program (CMP), within a private health plan in southern Brazil and show that such program is cost-effective and the return on investment (ROI) is positive. Methods: Using NAGIS© model and software for disease management program, the CMP was implemented in 211 patients (0.9% of the health plan beneficiaries). I compared health plan utilization and costs including CMP costs of one period of time before the program starts with the same period of time that the program was in place. Results: After 9 months of CMP, there were 162 patients. I considered outcomes for these 162 patients. For one Real invested, R$ 4,78 was saved (One 2008 American Dollar is 1,78 Brazilian Real). The average cost per enrollee per month reduced 45.9% (R$463,85 to R$250,89 ) and 39.4% (R$463,85 to R$280,90) if the program's costs (direct and indirect costs) are included as fixed costs. The number of visits reduced by 11.3% (794 to 704), as well as the labs exams which reduce 35.7% (420 to 270). Nevertheless, the labs exams per visit index reduce by 27.5%, where almost 53% of the visits had at least one exam before starting the program against 38.3% after the same period of time that the program starts. The number of hospitalizations reduced 34.6%, from 483 to 316. Thus, the bed-days saved were 554 days at infirmaries and 62 days at intensive care unit. The incremental cost per bed-day saved was R$419,66. Conclusion: The NAGIS© model of managed high cost patient, called Case Management Program is cost-effective where the incremental cost per bed-day saved is $ 419,66, and its return of investment is highly positive.