Governing Laws and Regulations for PTSD The establishment of service connection for PTSD has unique evidentiary requirements. It generally requires: (1) medical evidence diagnosing the condition in accordance with 38 C.F.R. § 4.125(a) (i.e., DSM-IV); (2) credible supporting evidence that the claimed in-service stressor actually occurred; and (3) medical evidence of a link between current symptomatology and the claimed in-service stressor. 38 C.F.R. § 3.304(f). See also Cohen v. Brown, 10 V