Trombley MJ, et al. - Medicare claims and enrollment data for a group of fee-for-service beneficiaries who had been assigned to 41 Accountable Investment Model (AIM) Accountable Care Organization (ACO) and for a comparable group of beneficiaries who stayed in the ACO markets but were served principally by non-ACO providers were assessed by researchers to determine the early effects of an ACO Model for underserved areas. Provider participation in AIM was correlated with a differential decrease in total Medicare spending of $28.21 per beneficiary per month corresponding to the comparison group, which amounted to an aggregate reduction of $131.0 million. The Centers for Medicare and Medicaid Services (CMS) made $76.2 million in prepayments and paid an extra $6.2 million in shared savings to ACOs, in which shared savings surpassed the prepayments over the same period. The aggregate net decrease was $48.6 million, which corresponded to a net decrease of $10.46 per beneficiary per month, following the accounting for this $82.4 million in CMS spending. Reductions in the number of hospitalizations and use of institutional post-acute care provided to the noted decline in overall spending. Therefore, cooperation in ACO shared savings contracts by providers serving rural and underserved areas was correlated with lower Medicare spending vs non-ACO providers, with up-front investments.