Background <p>Smoking has a great impact on oral health status of the patients. As universal adhesives have become a routine dental adhesive choice, understanding the potential impact of smoking on their clinical performance is crucial. This study aimed to determine the 18-month clinical performance of a universal adhesive used with different application modes in non-carious cervical lesions(NCCLs) of smokers and non-smokers.</p> Methods <p>This double-blind, randomized, split-mouth superiority clinical trial included 47 participants(24 non-smokers and 23 smokers) presenting with at least three NCCLs. A total of 228 NCCLs were categorized in line with the smoking status of the participants and universal adhesive(G-Premio BOND) application modes (Etch&amp;Rinse[ER], Selective-Etch[SLE] or Self-Etch[SE]). Randomization was performed at the lesion level, such that within each participant, each non-carious cervical lesion was randomly assigned to one of the three adhesive application modes. Restorations were evaluated at baseline, 6, 12 and 18-months using modified USPHS criteria and patient-reported hypersensitivity was assessed using a 0–10 visual analog scale(VAS) by two calibrated examiners blinded to group allocation. The primary outcome was retention. Secondary outcomes included marginal adaptation, marginal discoloration, color match, postoperative sensitivity and patient-reported postoperative hypersensitivity(VAS). Data were analyzed using Cochran’s Q, chi-square, Mann-Whitney-U and Kaplan–Meier tests(<i>p</i> &lt; 0.05).</p> Results <p>Among the non-smokers, one restoration from the SE and one from the ER group were lost, creating no significant difference regarding retention(<i>p</i> &gt; 0.05). At 18-months, no difference was detected among the application modes within each group for all USPHS criteria(<i>p</i> &gt; 0.05). Kaplan–Meier survival analysis revealed no significant difference in 18-month retention between smokers and non-smokers (<i>p</i> = 0.59). Overall restoration success at 18 months was 100% in smokers and 99.1% in non-smokers (ER 97.5%, SLE 100%, SE 97.5%) Statistically significant differences between smokers and non-smokers were detected only for marginal discoloration at 6 months in the ER group and at 12 and 18 months in the SE group(<i>p</i> &lt; 0.05). Both marginal discoloration and adaptation exhibited significant changes over time in both groups(<i>p</i> &lt; 0.05). VAS scores for postoperative sensitivity were significantly higher in smokers than in non-smokers at all follow-ups(<i>p</i> &lt; 0.05), except for the SE group(<i>p</i> &gt; 0.05).</p> Conclusion <p>The 18-month clinical performance of restorations was found to be similar regardless of the universal adhesive application mode. Smoking status primarily influenced marginal discoloration and patient-reported postoperative hypersensitivity.</p> Clinical trial registration <p>The study was registered with clinicaltrials.gov retrospectively registered (protocol number NCT04807465) on 03.13.2021.</p>