The effect of an adhesive bonding system on wear of posterior resin composite restorations was investigated using an in vitro three-body wear test. Resin composite restorations were placed with an adhesive system (Syntac) in Class I cavities on occlusally flattened extracted molars. Control restorations were prepared with the same resin composites but without etching or bonding. The surface of each restoration was replicated with poly(vinyl siloxane) for epoxy dies at baseline and after every 100,000 cycles until the completion of 400,000 wear cycles. The generalized wear (contact-free wear) of the composite restorations was scanned and traced at the same stag e of replication with a profilometer. The use of an adhes ive system significantly reduced the wear rate of the resin composites used in this study.