Purpose: The aim of this randomized, controlled, single-center, split-mouth clinical trial was to evaluate the clinical performance of a self-adhesive flowable composite resin (SAFC) in noncarious cervical lesions in comparison with a nanohybrid composite applied with a three-step etch-and-rinse adhesive system (E&Ra/nanoC). Materials and Methods: Eighty noncarious cervical lesions were included and assigned to one of two groups according to the split-mouth design. The cervical lesions in the experimental group were restored with an SAFC (Fusio Liquid Dentin), while a nanohybrid composite (G-aenial) applied with a three-step etch-and-rinse adhesive system (Optibond FL) was used for the control group. Clinical evaluation was performed after 1 week and again at 6 months according to FDI criteria. Data were analyzed using Wilcoxon Signed Rank and Mann-Whitney U-tests (α = 0.05). Results: After 6 months, 27 of the 40 SAFC restorations were in clinically unacceptable condition due to retention failure; this corresponded to a success rate of 33% compared to the success rate of 100% for the E&Ra/ nanoC restorations (p 0.05). For other criteria examined, the difference between the two groups was only statistically significant for color and translucency (p 0.05). Conclusion: The clinical performance of the SAFC was found to be unacceptable after 6 months of clinical use. Keywords: self-adhesive flowable composite, noncarious cervical lesions, nanohybrid composite