Objectives: The involvement of arginine-vasopressin (AVP) in animal and human aggression has been well established in the literature. Recent research has shown an association between the minor allele (C) of single-nucleotide polymorphism rs35369693 located on the AVP 1B receptor gene and childhood aggression. Materials and methods: The present study sought to replicate the association between rs35369693 and aggression using a sample of clinically referred children (N = 141) with behavioural problems. Results: Analyses confirmed a significant relationship between the minor C allele on rs35369693 and teacher-rated reactive aggression. Although males had significantly greater aggression than females on three of the four measures, sex was not shown to moderate the effect of the C allele on any of the aggression measures. Conclusion: These findings reinforce the results from previous research and also suggest that the associations of the AVP 1B receptor may be specific to reactive, emotional rather than proactive or callous types of aggression.