d ) . In addition to the general requirements for service connection , PTSD claims require : ( 1 ) medical evidence diagnosing the condition ; ( 2 ) a link , established by medical evidence , between current symptoms and an in - service stressor ; and ( 3 ) credible supporting evidence that the claimed in - service stressor occurred . 38 C . F . R . § 3 . 304 ( f ) . A diagnosis of PTSD must be established in accordance with 38 C . F . R . § 4 . 125 ( a ) , which provides that all psychiatric diagnoses must conform to the American Psychiatric Association ' s Diagnostic and Statistical Manual for Mental Disorders . 38 C