Objectives: The aim of this study was to evaluate the mikroleakage of four fissure sealants in relationship to fissure configuration after articfical aging. Methods: 843 fissures of extracted non-carious molars sealed with either Ultraseal XT, Conseal f, Smartseal or Delton were examined. Following prophylaxis with Klint, the fissure sealant was applied as recommended by the manufacturer. One half of the teeth was thermocycled (5-55 degree celsius, 5000 cycles). Following that, all teeth were immersed in methylene blue for 48 hours, rinsed, sectioned and examined with digital light microscopy (10-200x). Fissures were characterized as U, V, I and IK based on their cross-sectional shape. Microleakage was scored as 0= no dye penetration; 1= dye penetration into the occlusal third of the enamel-sealant interface; 2= dye penetration into the middle third of the interface; and 3= dye penetration into the apical third of the interface. Results: Following mikroleakage scores were evaluated. Regardless of the fissure configuration, significantly higher average microleakage scores were obtained after thermocycling (p 0.001, ANOVA). In particular, Smartseal yielded the highest microleakage scores after artifical aging (p 0.05, Tukeys test). Conclusions: Within the limitations of the present study, it can be concluded that artifical aging increased microleakage of the four fissure sealants significantly. Keywords: microleakage, fissure sealants, artificial aging, fissure configuration