This clinical study was designed to determine whether the thickness of the flap can influence root coverage when gingival recessions associated with traumatic toothbrushing are treated using a coronally advanced flap (CAF). Nineteen patients, aged from 25 to 57 years, with high levels of oral hygiene (full-mouth plaque scores <20%) were selected for the study. Each patient contributed with one Miller Class I or II maxillary or mandibular recession. A total of 19 recessions > or =2 mm were treated. After local anesthesia and before flap elevation, the exposed root surface was planed with a sharp curet. A trapezoidal full- and partial-thickness flap was then elevated, displaced coronally, and sutured to cover the treated root surface. Before suturing, flap thickness was measured in the alveolar mucosa with a gauge. After surgery, all patients were recalled for control and professional prophylaxis once a week during the first month and monthly up to the third month. The mean initial recession depth was 3.0+/-0.9 mm. Mean flap thickness (FT) was 0.7+/-0.2 mm. Three months later, mean recession depth was 0.6+/-0.6 (P <0.0001) and mean recession reduction was 2.4+/-0.7 mm. Mean root coverage was 82+/-17%. Flap thickness >0.8 mm was associated with 100% of root coverage. The results of this study indicate that there is a direct relation between flap thickness and recession reduction (P <0.0001).