The aim of this study was to assess the microleakage of a pit-and-fissure sealant after classical enamel preparations (prophylaxis followed by acid etching alone and mechanical widening with bur) and after air abrasion. Ninety noncarious freshly extracted third molars were randomly assigned to three groups of 30. In each group, the mesial halves of the fissures were treated with air abrasion and conditioned with acid etching for 15 s. In group 1, the distal halves were treated with acid etching alone. In group 2, the distal halves of the fissures were widened mechanically with a bur and etched for 15 s. In group 3, the distal halves were prepared with air abrasion alone. Then the sealant (Clinpro) was applied on the occlusal fissures of all teeth, according to the manufacturer's recommendations. The teeth were thermocycled and the samples placed in a 1% methylene blue dye solution. The teeth showing microleakage and the means of infiltration were assessed with an image analysis system. The microleakage of sealants prepared with air abrasion alone displayed significantly greater microleakage (80%) (p 0.0001) than the ones placed after prophylaxis and etching (13.33%), bur and etching (20%), or air abrasion and etching (22.2%). The samples prepared with air abrasion alone also showed the highest mean microleakage (1.14 ± 1.4 mm) when compared to samples receiving prophylaxis and acid etching (0.12 ± 0.41), bur and acid etching (0.08 ± 0.26), or air abrasion and acid etching (0.09 ± 0.4) (p 0.05). No significant difference was noted between the three types of enamel preparation when etching was performed. Air-abrasion treatment does not eliminate the need for etching the enamel surface before applying the sealant. Keywords: microleakage, air-abrasion, etching, sealant