Buildings with masonry infill walls (MIWs) in reinforced concrete (RC) frames are commonly used all around the world. It is well known that infill walls may affect the strength, stiffness, and displacement ductility of the structural system. Different approaches have been adopted in different codes and guidelines to consider the stiffness and strength contribution of MIWs on RC frame behavior. This study compares the ability of the existing guidelines to estimate stiffness, strength, and deformability of RC frames with MIWs by using a compiled experimental database composed of 51 experiments from 24 different studies. Alternative expressions are proposed in this study to provide improved estimates of stiffness and deformability of infilled RC frames. (C) 2014 American Society of Civil Engineers.