Objective: The use of self-etch adhesives has increased in spite of reports of deficient enamel bonding. Some clinicians etch enamel separately to circumvent this shortfall. Therefore, the objective of this study was to assess the influence of acid-etching on the enamel sealing of 3 self-etch adhesives after thermal fatigue. Method and Materials: Two box-type preparations were restored in each of 30 bovine incisors with 1 of 3 selfetch adhesives: Adper Prompt L-Pop (3M ESPE); Clearfil SE Bond (Kuraray America); or iBond (Heraeus Kulzer), with and without phosphoric acid enamel etching, followed by Filtek Z250 (3M ESPE). After half of the restorations were fatigued for 1,500 thermal cycles, marginal sealing was challenged with 50% ammoniacal silver nitrate. Silver penetration was ranked from 0 to 4 and interfaces analyzed under a field-emission scanning electron microscope (FESEM) with a backscattered detector. Nonparametric statistical analyses were carried out at a 95% confidence level. Results: Clearfil SE Bond resulted in significantly less enamel leakage than the other 2 self-etch adhesives. Acid etching significantly reduced silver infiltration for all adhesives when specimens were thermocycled. When specimens were not thermocycled, acid etching only reduced silver infiltration for iBond. Under the FESEM, silver deposition was observed inside the adhesive layer for Adper Prompt L-Pop and iBond. For Clearfil SE Bond only 2 of 10 specimens displayed silver infiltration along the enamel-adhesive interface. Conclusion: Etching with phosphoric acid improved the enamel marginal sealing of the 3 self-etch adhesives when specimens were subjected to thermal fatigue. Keywords: dental leakage, enamel etching, scanning electron microscopy, self-etch adhesives