Purpose: The aim of this blinded, randomized, prospective long-term study was to evaluate the clinical performance of the two-step self-etching adhesive AdheSE (AS, Ivoclar Vivadent) compared to the etch-and-rinse adhesive system Excite (EX, Ivoclar Vivadent) in combination with the hybrid resin composite Tetric Ceram HB (Ivoclar Vivadent) for Class I and II restorations. Materials and Methods: In accordance with a split mouth design, 50 patients received 100 restorations in premolars and molars. The restorations were assigned at random to the self-etching (AS) or the etch-and-rinse (EX) group. Each restoration was scored according to the modified Ryge criteria at baseline and after 6, 12, 24 and 48 months. Epoxy resin replicas of 60 restorations were made at each observation period for an additional SEM analysis of the occlusal margins. Results: After 4 years, 60 of 100 restorations could be evaluated. The cumulative survival rate for group EX was 100% and for group AS 96.7%. One restoration in group AS had failed due to marginal gap formation. For the criterion marginal adaption in group AS, significantly more bravo ratings (30%) were observed after 4 years compared to group EX (6.7%) (p 0.05; Mann-Whitney U-test). The results of the SEM margin analysis revealed no significant differences between groups AS and EX (Mann-Whitney U-test; p > 0.05). Conclusion: Both adhesive systems performed satisfactorily over the four-year observation period. A significant deterioration over time was found for the criterion marginal adaption in AdheSE. Keywords: clinical study, self-etchinging adhesive, flowable composite, Ryge criteria, composite resin