The aims of this study were: (a) to examine associations of oxytocin receptor gene (OXTR) single nucleotide polymorphisms (SNPs) with post-traumatic stress disorder (PTSD) and dissociative symptoms and (b) to investigate gene–environment (G × E) interaction with childhood maltreatment. Salivary DNA samples from 228 women of European ancestry were analysed. Two SNPs, rs237895 and rs237897, were associated with dissociative symptoms but not PTSD diagnosis. Another SNP (rs2254298) was associated with dissociation when interacting with history of childhood maltreatment. These results contribute to theorising and evidence suggesting that the oxytocin system and its genetics may be associated with risk for dissociation among European American women, including those with maltreatment history. Replication with larger patient samples, including men and other ancestry groups, is needed.