Introduction School victimization by peers is an important social problem with serious short- and long-term consequences poorly studied at preschool ages, which can lead to school bullying without timely intervention. Longitudinal data was used to determine the prevalence of warning signs of preschool peer victimization and its individual and family risk factors. Methods Data was obtained from 577 community preschoolers. School victimization was measured using the Strengths and Difficulties Questionnaire (SDQ) administered to parents and teachers of children at ages 4 and 5. Risk factors for the child (demographics, conduct and emotional problems, aggressiveness) and the family (maternal problems during pregnancy and early development, parenting styles, adaptive functioning and parents’ problems) were previously recorded at 3 years old. Results Combined information from parents and teachers showed that 4.2% of preschoolers presented warning signs of victimization at ages 4 and 5. Low socioeconomic status, poor emotional control, early problems making friends and low level of parenting education in social norms at age 3 predicted later victimization at ages 4 and 5 (AUC = .78). Conclusion Peer victimization affects a considerable percentage of preschoolers. Early detection may help to reduce the risk of escalation.