Aim: To evaluate the use of different surface preparations and a new self-etch primer to enhance the shear strength of orthodontic brackets bonded to composite surfaces. Methods: One hundred and twenty composite resin cylinders were used. The cylinders were mounted and randomly divided into eight groups, according to the surface preparation (none, bur, microetching, or silane) and the acid/primer combinations (phosphoric acid/sealant or selfetch primer). Results: The results of the analysis of variance comparing the groups tested (F = 54.735) indicated that there was a significant difference (P = .0001) between the eight groups. The four groups with the composite surface etched with 37% phosphoric acid and a sealant had significantly higher shear bond strengths than the groups in which the acid-etch primer was used, regardless of the type of surface preparation employed. Within the four groups treated with phosphoric acid and sealant, surface preparation using a finishing bur provided the highest shear bond strength (mean = 9.4 ± 1.3 MPa). This was significantly stronger than the group in which the composite surface was left intact, ie, control (mean = 6.1 ± 2.7 MPa). On the other hand, the sandblasting (mean = 7.8 ± 2.2 MPa) and silane (mean = 7.8 ± 2.3 MPa) groups were not significantly different from each other or from the other two groups. Conclusion: The use of a phosphoric acid etch, followed by a sealant before bonding orthodontic brackets to composite surfaces produced significantly greater shear bond strength than that achieved with the use of the self-etch primer. The most reliable bonding procedure to composite surfaces is to prepare the surface with a finishing bur, together with the use of 37% phosphoric acid and a sealant, before bonding the bracket with the adhesive. World J Orthod 2003;4:343–347.