Part I of this article ("Six Design and Implementation Lessons," Physician Executive, Sept.-Oct. 1993, pp. 46-50) described an ambulatory utilization review (AUR) program designed and implemented by Metropolitan Life Insurance Company and reviewed some of the lessons learned over the past five years. Those lessons pertained to the tasks of inventing a new information technology to measure and evaluate ambulatory care and some of the practical implementation issues associated with review of 30,000 small dollar value claims per day in 19 claim offices nationwide. This article turns to the basic purpose of AUR--to review the medical necessity and appropriateness of ambulatory utilization. One lesson learned about AUR in this context is that AUR works: savings from the program outweigh costs by almost 5:1. The more important lessons, however, stem from understanding how the savings are achieved, and what some of the other unintended benefits of the program are.