In this in vitro study we evaluated the microleakage (entrance of microorganisms and toxins between the restoration and cavity walls of teeth) of Class V (kidney-shaped) cavities restored with four different types of restorative materials: a reinforced glass-ionomer cement, a resin-modified glass-ionomer cement, a compomer, and an ormocer. The effects of dental fluorosis and salivary contamination on microleakage of these materials were compared in primary molar teeth. Ninety-six Class V cavities were prepared on the buccal and lingual/palatinal surfaces of 48 non-carious human primary molars, half of which had fluorosis TFI (Thystrup and Fejerskov index) scores of 4. In both the fluorosed and control group, teeth were randomly assigned to two subgroups of 12. The first twelve teeth in each group were salivary contaminated prior to restoration. All restorations were placed strictly according to the instructions of the manufacturers. The samples were immersed in methylene blue, embedded in acrylic resin, sectioned and analyzed using stereomicroscopy. Statistically significant difference between the fluorosis and nonfluorosis groups was observed only for the gingival margins (p=0.021). Of the restorative materials tested, the resin-modified glass-ionomer cement was found to be more effective than the other materials in reducing microleakage both in the presence of fluorosis and salivary contamination.