Purpose: To compare the occlusal and gingival microleakage of Class-II composite restorations utilizing etch-and-rinse and self-etch adhesives and different liner materials in primary and permanent teeth. Study design: Standardized class-II cavities were prepared in freshly-extracted sound primary and permanent molars (n=80/each), with all cavosurface margins involving enamel. The main experimental groups were; A. Single Bond 2/primary teeth; B. Adper SE Plus/primary teeth; C. Single Bond 2/permanent teeth; and D. Adper SE Plus/permanent teeth. Each group comprised 4 subgroups (n=10/each) with respect to the liner material employed (n=10/subgroup): I. Fuji VII; 2. Fuji Triage; 3. Filtek Supreme XT Flowable Composite, and 4. No liner. All teeth were restored with Filtek Supreme XT Universal Nanofilled Composite. Following thermocycling and immersion in basic fuchsin, the extent of microleakage was measured on crown sections using image analysis. The data were analyzed with Wilcoxon Signed Ranks Test, Mann-Whitney U-Test and Kruskal-Wallis One-Way ANOVA at alpha=0.05. Results: In both primary and permanent teeth the use of etch-and-rinse adhesive resulted in similar occlusal and gingival microleakage values (p>0.05). As for the self-etch adhesive, similar results were observed (p>0.05) with the exception of significantly less occlusal leakage in the Fuji Triage VII and Fuji Triage subgroups of primary teeth than those of permanent teeth (p<0.05). When the effects of liner material and the type of adhesive were disregarded, significantly more gingival microleakage was observed in primary teeth than in permanent teeth (p<0.01), while the occlusal microleakage values were similar (p>0.05). Irrespective of the tooth type and adhesive material, comparison of subgroups containing a liner material with those without one revealed no significant differences for both occlusal and gingival microleakage values (p>0.05). Conclusions: Occlusal microleakage was similar in both primary and permanent teeth, while a lesser extent of gingival seal was observed in primary teeth. Overall, placement of a liner material did not improve resistance to microleakage.