( d ) . Service connection for PTSD requires medical evidence diagnosing the condition in accordance with 38 C . F . R . § 4 . 125 ( a ) ; a link , established by medical evidence , between current symptoms and an in - service stressor ; and credible supporting evidence that the claimed in - service stressor occurred . 38 C . F . R . § 3 . 304 ( f ) . Effective July 13 , 2010 , VA amended the regulations for adjudicating disability compensation claims for PTSD in 38 C . F . R . § 3 . 304 ( f ) ( 3 ) to liberalize the evidentiary standard for establishing the required in - service stressor in certain