- service incurrence or aggravation of a disease or injury ; and ( 3 ) a causal relationship , i . e . , a nexus , between the claimed in - service disease or injury and the current disability . Holton v . Shinseki , 557 F . 3 d 1362 , 1366 ( Fed . Cir . 2009 ) . Service connection may also be granted for any disease diagnosed after discharge when all of the evidence establishes that the disease was incurred in service . 38 C . F . R . § 3 . 303 ( d ) . In addition to the general requirements for service connection , PTSD claims require : ( 1 ) medical evidence diagnosing the condition ; ( 2