This article presents the outcomes of a recent study carried out among engineering professionals and academics in Egypt to propose a criteria-based energy efficiency rating system for existing buildings. It discusses the use of a multiple criteria decision making technique, namely the Analytic Hierarchy Process (AHP), for developing the weights of the proposed rating system criteria, and generally reviews the use of AHP to develop building energy rating systems. While the AHP approach of criteria weighting was applied in other countries, the present study distinctively applied it to developing a proposed rating system for existing buildings in Egypt. In this study, nine energy rating criteria were identified by thoroughly comparing and analyzing internationally established green building / sustainability rating systems for existing buildings such as LEED, BREEAM, Green Globes, Energy Star, IGBC and Pearl rating system for Estidama. A survey was then conducted to collect the opinions of Egyptian engineering professionals regarding the relative priority of the identified criteria, and to determine, according to the opinions of participants, which criteria are mandatory and which are optional for existing buildings seeking to become 'greener'. Using AliP, weights were developed for the optional criteria, representing their relative importance. Based on the performed analysis, the resulting rating criteria are: one mandatory prerequisite, which is the Minimum Energy Performance, and eight optional credits with descending relative weights, which are: Use of Renewable Energy Sources, Building Envelope Efficiency Strategies, Use of Energy Efficient Appliances and Equipment, Building Systems Automation and Controllability, Eco-friendly Refrigerants & Fire Suppression Systems, Operation and Maintenance Practices, Metering and Sub-metering of Building, zones and systems and finally Building-related Transportation Impact.