Purpose: To compare the effects of quartz-tungsten-halogen (QTH) and light-emitting-diode (LED) curing units on the 3-year clinical performance of a nanofilled composite resin in noncarious cervical lesions. Materials and Methods: Twenty-six patients with at least 2 noncarious cervical lesions were enrolled in the study. A total of 154 restorations were placed: half polymerized with QTH and half polymerized with LED. Single Bond was used as the adhesive and Filtek Supreme was used as the restorative material for all restorations. The restorations were assessed by two different examiners using modified Ryge/USPHS criteria at baseline and at 6, 12, 24, and 36 months. The survival rates were analyzed with the Kaplan-Meier estimator and the Log-Rank test, and the statistical analysis was completed using Pearson's chi-square test (p 0.05). Results: Twenty patients were available for recall after 3 years and 114 restorations were evaluated (recall rate of 74%). The survival rate was 84% for QTH and LED polymerized restorations. There were no statistically significant differences in survival rates between the light-curing units (p > 0.05). No significant differences were observed between QTH and LED polymerized restorations in terms of any of the evaluation criteria at the end of 3 years (p > 0.05). No color change in the restorations was observed and none of them exhibited secondary caries at the end of 3 years. Conclusion: Over the 3-year study period, both curing units, QTH and LED, produced acceptable clinical results in noncarious cervical lesions. Keywords: light-curing unit, composite resin, clinical evaluation