Regulations governing the renewal of licenses for commercial nuclear power plants require that the aging of certain passive plant components be managed. This is normally addressed through the development and adoption by the plant of an aging management program. These programs are reviewed by the NRC as part of the license renewal process. During these reviews it became apparent to the NRC that sufficient information regarding the degradation of pressurized water reactor internals was not available to provide reasonable assurance that aging of these components would be adequately managed during the period of extended operation. To fill this knowledge gap the nuclear industry developed MRP-227 Rev. 0 "Pressurized Water Reactor (PWR) Internals Inspection and Evaluation Guidelines". This paper provides some insights into the need for information concerning PWR internals the development and contents of the guidelines the NRC's review of those guidelines and the proposed implementation of those guidelines.