Background: The neuropeptides oxytocin and vasopressin have recently been implicated in the aetiology of autism. Both have effects on behaviour and physiology especially in relation to social bonding. Furthermore, both are modulated by the sex hormones, which heighten their candidacy for a role in autism where the ratio of affected males to affected females is highly skewed (4:1). Objectives: To examine the genetic variation within the oxytocin and vasopressin receptor in the Irish autism sample. Methods: Tagging SNPs in the oxytocin receptor (OXTR) and VNTRs in the arginine vasopressin receptor 1A (AVPR1A) were analyzed in the Irish autism sample, a sample of 179 parent-child trios. Results: Prior to correction for multiple testing, associations between OXTR and autism were found with 3 markers (rs11720238 p=0.031, rs7632287 p=0.0076, and rs4564970 p=0.0091). Two SNPs in OXTR showed association with a high functioning subset of the sample after a multiple permutation testing (rs11720238 p= 0.025 and rs7632287 p=0.0042) based on a cluster analysis of the clinical sample. Conclusions: These results confirm the importance of oxytocin receptor in the aetiology of autism.