The aim of the study is to evaluate the influence of surface-treatment methods with and without the use of a retention hole on the shear bond strength of a resin composite adhered to amalgam using an adhesive system. Amalgam specimens were divided into six groups. Group 1 (Bur) specimens were roughened with a diamond bur, Group 2 (Al2O3) specimens were sandblasted with a 50 m aluminum oxide powder, Group 3 (CoJet (R)) specimens were sandblasted with 30 mu m CoJet (R) Sand, Group 4 (Bur + Rh) specimen surfaces were prepared with a retention hole 1 mm in diameter and 1 mm deep and roughened with a diamond bur, Group 5 (Al2O3 + Rh) specimens were also prepared with a retention hole and sandblasted with 50 mu m aluminum oxide powder, and Group 6 (CoJet (R) + Rh) surfaces were prepared with a retention hole and sandblasted with 30 mu m CoJet (R) Sand. Resin composite cylinders were bonded onto the amalgam surfaces using Xeno (R) IV, Optibond (TM) All-In-One, Clearfil (TM) SE Bond, Adper (TM) Single Bond Plus, and Scotchbond (TM) Multi-Purpose adhesive systems. In addition, silane (Monobond S) was used for Groups 5 and 6. The shear bond was determined and statistically analyzed using two-way analysis of variance and post hoc Tukey's tests (p <= 0.05). The surface treatment significantly affected the shear bond strengths of the adhesive systems. The shear bond strengths of Optibond (TM) All-In-One (2.661 +/- 0.48 MPa) in Group 1 and Scotchbond Multi-Purpose (3.818 +/- 0.98) in Group 4 were significantly higher than those of the other adhesive systems. Silica coating of the amalgam surface significantly improved the shear bond strength of the resin composites. The addition of a retention hole on the amalgam affects the bonding strength of the composite adhesion.