The purposes of the present study were: 1) to assess the microleakage at the cervical margin of Superbond-lined composite restorations with and without a cervical amalgam base and compare the results to cervical margins of composite restorations lined with Scotchbond 2, and 2) to compare the quality of the occlusal margins of Superbond-lined P-50 restorations with those bonded with Scotchbond 2. Forty-eight class 2 cavities were prepared in extracted or exfoliated primary molars. The teeth were randomly divided into three groups and restored as follows: Group A, amalgam + Superbond + P-50 (sandwich); Group B, Superbond + P-50; Group C, Scotchbond 2 + P-50 (control). Marginal leakage was assessed by the degree of dye penetration on sections of the restored teeth. The occlusal margins presented no or minimal leakage (degrees 0 and 1) in 53% of Group A restorations, 60% of Group B, and 44% of Group C. These differences were not statistically significant (P<0.05). The cervical margins showed moderate to severe dye penetration (degrees 2 and 3) in 94% of Group A, 47% of Group B, and 87% of Group C. These differences were statistically significant (P<0.05). The amalgam/Superbond/composite interface exhibited no leakage in 70% of the restorations. Although marginal leakage was not completely eliminated, Superbond exhibited significantly less leakage (P<0.05) at the cervical margins than Scotchbond 2 or amalgam with Superbond.