To assess the microleakage of a pit and fissure sealant after preparing enamel with sono-abrasion, used alone or associated with acid etching. This technique was compared with classical enamel preparations i.e. acid etching and diamond bur associated with etching. Ninety 3rd molars were used. In the mesial halves, the fissures were prepared with sono-abrasion and acid etching for 15 seconds. Then, the samples were randomly assigned to three groups of 30. They were either treated with acid etching alone (group 1), widened mechanically with a bur and etched for 15 seconds (group 2) or prepared with sono-abrasion alone (group 3). Then, the resin-based sealant was applied according to the manufacturer's recommendations. The teeth were thermocycled and placed in a 1% solution of methylene blue. The teeth showing microleakage and the means of infiltration were assessed with an image analysis system. The poorest results were obtained with sono-abrasion alone which showed a greater number of specimens with microleakage (73.3%) (p 0.001). They also showed the highest mean of microleakage (0.85 ± 0.79 mm vs 0.1 ± 0.26 for acid; 0.35 ± 0.85 for bur associated with etching p 0.0001); and 0.19 ± 0.45 for sono-abrasion associated with etching. No significant difference was noted between the three types of enamel preparation using etching. Sono-abrasion can be used for preparing dental enamel prior to sealing the tooth but it does not eliminate the need for etching. Keywords: sealant, sono-abrasion, microleakage, SEM