Background: The aim of this study was to clinically evaluate the treatment of Class I gingival recessions by coronally positioned flap with or without acellular dermal matrix allograft (ADM). Methods: Thirteen patients with comparable bilateral Miller Class I gingival recessions (greater than or equal to3.0 mm) were selected. The defects were randomly assigned to one of the treatments: coronally positioned flap and acellular dermal matrix (ADM group) or coronally positioned flap alone (CPF group). The clinical parameters included: probing depth (PD), clinical attachment level (CAL), recession height (RH), recession width (RW), height of keratinized tissue (HKT), thickness of keratinized tissue (TKT), plaque index (PI), and gingival index (GI). The measurements were taken before the surgeries and after 6 months. Results: The mean baseline recession was 3.4 mm and 3.5 mm for ADM group and CPF group, respectively. After 6 months, both treatments resulted in significant root coverage (P <0.01), reaching an average of 2.6 mm (76%) in the ADM group and 2.5 mm (71%) in the CPF group. The difference in recession reduction between treatments was not statistically significant. There were no statistically significant differences between the treatments in PD, CAL, RH, RW, and HKT. However, the mean TKT gain was 0.7 mm for the ADM group and 0.2 mm for the CPF group (P <0.01). Conclusion: It can be concluded that both techniques could provide significant root coverage in Class I gingival recessions; however, a greater keratinized tissue thickness can be expected with ADM.75811371144