Background.Epigenetic differences exist between trauma-exposed individuals with and without post-traumatic stress disorder (PTSD). It is unclear whether these epigenetic differences pre-exist, or arise following, trauma and PTSD onset.Method.In pre- and post-trauma samples from a subset of Detroit Neighborhood Health Study participants, DNA methylation (DNAm) was measured at DNA methyltransferase 1 (DNMT1), DNMT3A, DNMT3B and DNMT3L. Pre-trauma DNAm differences and changes in DNAm from pre- to post-trauma were assessed between and within PTSD cases (n = 30) and age-, gender- and trauma exposure-matched controls (n = 30). Pre-trauma DNAm was tested for association with post-trauma symptom severity (PTSS) change. Potential functional consequences of DNAm differences were explored via bioinformatic search for putative transcription factor binding sites (TFBS).Results.DNMT1 DNAm increased following trauma in PTSD cases (p = 0.001), but not controls (p = 0.067). DNMT3A and DNMT3B DNAm increased following trauma in both cases (DNMT3A: p = 0.009; DNMT3B: p < 0.001) and controls (DNMT3A: p = 0.002; DNMT3B: p < 0.001). In cases only, pre-trauma DNAm was lower at a DNMT3B CpG site that overlaps with a TFBS involved in epigenetic regulation (p = 0.001); lower pre-trauma DNMT3B DNAm at this site was predictive of worsening of PTSS post-trauma (p = 0.034). Some effects were attenuated following correction for multiple hypothesis testing.Conclusions.DNAm among trauma-exposed individuals shows both longitudinal changes and pre-existing epigenetic states that differentiate individuals who are resilient versus susceptible to PTSD. These distinctive DNAm differences within DNMT loci may contribute to genome-wide epigenetic profiles of PTSD.