In this study, researchers wished to ascertain whether there were age (three- and four-year old), sibling (with or without older siblings), and sex (male and female) differences in the use of relational aggression in preschool students as rated by peers and teachers. In order to answer this research question, two 2 × 2 × 2 factorial ANOVA procedures with the relational aggression composite score as the dependent variable on the PSBS-P and PSBS-T were used for peer and teacher assessment, respectively, of relational aggression. Results revealed that in the peer ratings of preschool students' relationally aggressive behavior, there was an disordinal age by sibling interaction, in which four-year-old children with siblings were significantly more likely to be rated by their peers as using relational aggression than three-year-old children without siblings. In the teacher ratings of preschool students' relationally aggressive behavior, a main effect for age was observed. Teachers rated four-year old children as evidencing significantly higher levels of relational aggression as compared to three-year-olds. No sex differences were observed in the use of relational aggression either at age three or age four in this sample. Implications for these findings are presented.