Purpose: This study evaluated the marginal discrepancies and leakage of all-ceramic crowns cemented with different luting agents after fatigue tests. Materials and Methods: Forty-eight all-ceramic crowns were cemented onto natural molars. Zinc-phosphate cement, compomer cement, and an adhesive composite resin luting system were used in 16 specimens each. Sixteen metal-ceramic crowns were cemented with zinc-phosphate cement as a control. Half of the specimens in each group were fatigued in a chewing simulator for 600,000 loading cycles with 3,500 thermocycles. The others received the 3,500 thermocycles only. An impression-replica technique and SEM were used for evaluation of the marginal discrepancies. Leakage of the specimens was microscopically assessed. Results: There were no significant differences between marginal discrepancies of the groups, with the exception of porcelain shoulder margins in the metal-ceramic group, which had significantly larger discrepancies ( P .01). There was no significant effect of the fatigue tests on marginal discrepancies. However, significant differences of leakage were found between the groups cemented with the different luting agents after both fatigue tests. The adhesive composite resin luting system demonstrated the least leakage. The compomer cement showed an intermediate level of leakage, and the zincphosphate cement showed severe leakage that extended through the dentinal tubules to the pulp chambers. No significantly different effect of the two fatigue tests on the leakage was found. Conclusion: The adhesive composite resin luting system showed clinically acceptable marginal discrepancies and an excellent ability to minimize leakage of allceramic crowns.