Smoking is detrimental to periodontal tissues, and periodontal destruction is greater among smokers. Paradoxically, smokers seem to have less gingival bleeding than never-smokers with comparable supragingival plaque. There is scarce information about the impact of smoking on gingival crevicular fluid (GCF) volume. This single-arm study clinical trial assessed the effect of smoking on GCF volume during the treatment of gingivitis. The sample included 24 never-smokers (47.3 +/-6.7years old, 41.7% males) and 21 smokers (45.8 +/- 5.1 years old; 55% males; 19.6 +/- 11.8 cigarettes/day; 24.1 +/- 8.7 years of smoking) with gingivitis and chronic periodontitis. After baseline supragingival scaling, patients received oral hygiene instructions weekly for 180 days. Particqants were examined at baseline, 30, 90 and 180 days, and gingival bleeding index (GBI), bleeding on prob-ing (BOP), periodontal probing depth (PPD) and GCF volume were recorded. Statistical analysis was performed using linear models (Wald test, p<0.05%). Smokers had significantly smaller GCF volumes than never-smokers. This finding was not attributed to GBI, BOP or PPD. Higher volumes of GCF were significantly associated with deeper pockets. GCF was significantly reduced throughout the study for both smokers and never-smokers, and the largest reductions were seen at 30 days. Smoking affected the GCF crevicular fluid volume independently of the presence of gingival bleeding, BOP and PPD. Smoking status and PPD should be taken into account when GCG volume and components are under investigation.