Objective: The purpose of this investigation was to evaluate the microleakage of Class V lesions restored with a compomer material (Dyractflow) using 2 single-bottle bonding systems. Method and materials: Sixty-four Class V cavity preparations were made on 32 sound, extracted human premolars, 1 preparation on the facial surface and 1 on the lingual surface. Teeth were then randomly divided into 2 groups. Group 1, which served as the control group, was restored as follows: group 1a, facial surface with PQ1 single-bottle bonding system plus TPH resin composite; group 1b, lingual surface with Prime & Bond NT single-bottle bonding system plus TPH. Group 2 was restored as follows: group 2a, facial surface with PQ1 plus Dyractflow compomer material; group 2b, lingual surface with Prime & Bond NT plus Dyractflow. After 24 hours of storage in water and subsequent thermocycling, each specimen was immersed in 0.2% basic fuchsin dye for 24 hours. The teeth were sectioned longitudinally and horizontally, and dye penetration at enamel and cementum margins was viewed at 330 magnification by 2 independently calibrated evaluators. Specimens were evaluated as either having leaked or not having leaked. Results: No statistically significant differences in microleakage were noted between group 1 and group 2 specimens. Conclusion: Both single-bottle bonding systems, PQ1 and Prime & Bond NT, demonstrated equal effectiveness in reducing microleakage beneath compomer and composite restorations.