Purpose: To evaluate the sealing ability of etch-and-rinse and self-etching adhesives in Class V cavities before and after thermocycling in vitro. Materials and Methods: Etch-and-rinse adhesives (Prime & Bond NT [P&B], XP Bond [XPB], Scotchbond 1 XT [SBX], Syntac [SYN]) and self-etching adhesives (Xeno III [XNO], i-Bond [IBO], Clearfil SE Bond [CLF]) were used. A microleakage test was performed to evaluate marginal sealing. Seventy molars were divided into seven groups according to the adhesive used. Class V cavities were restored and each group was divided into two subgroups. One group was water immersed for 24 h and the other was thermocycled. Then, specimens were immersed in fuchsin and sectioned. Microleakage and dentin permeability were recorded on occlusal and gingival walls and data were statistically analyzed. Results: Etch-and-rinse adhesives provided perfect occlusal sealing. Self-etching adhesives obtained slight occlusal leakage. In the gingival wall, XNO and CLF showed the lowest leakage, followed by XPB and SBX, then P&B. SYN and IBO exhibited the highest leakage. All SE adhesives and XPB provided sealed dentinal tubules. Thermocycling did not affect the occlusal sealing but reduced the gingival sealing when P&B, SYN, XNO, CLF, and IBO were used. Conclusion: In enamel, marginal leakage was prevented when phosphoric acid was used. Self-etching adhesives promoted slight occlusal leakage. The gingival sealing was poorer than the occlusal sealing. XNO, CLF followed by XPB obtained the best gingival sealing. Thermocycling did not affect the occlusal bonding but reduced the gingival sealing, except when XPB and SBX were used. Schlagwörter: adhesives, Class V sealing, thermocycling, in vitro