Abstract: Through utilization review (UR), managed care organizations (MCOs) monitor and alter physician treatment decisions. We show that the value of UR depends on physician incentives. Not surprisingly, when physicians have incentives to significantly overtreat patients, UR can improve social welfare by eliminating unnecessary utilization. More surprisingly, UR can also improve welfare when physicians have incentives to significantly undertreat patients. In this case, UR filters out the least valuable cases, encouraging physicians to recommend more treatments. We also show that the effectiveness of UR depends on MCO precommitment to a treatment approval threshold. Ex ante optimal precommitment can make it appear that the MCO is inappropriately withholding care ex post.