When a military service veteran files a claim for disability compensation with the VA for an illness or disability that resulted from military service, one of the first things a veteran has to establish is that the current illness or disability is connected to the veteran's military service. This is called "establishing service connection."
Here are the five methods of establishing service connection for a current disability, disease, or illness.
Direct Service Connection. While a direct service connection can be established in any number of ways, it generally means there is clear evidence of an incident that occurred while the veteran was in service as well as evidence of “linkage” between the incident and the lasting disability. Here is an example: A veteran is paralyzed from the waist down. In military service, the veteran suffered an injury in Airborne School, breaking his back during a parachute landing. In this example, the veteran's paralysis is clearly connected to his military service.
Presumed Service Connection. Certain conditions or diseases are "presumed" to be service-connected. The VA has lists of conditions that are presumed to be related to service and their presumptive periods. For example, any veterans who were exposed to Agent Orange during their military service and who now have Parkinson's disease are presumed to have a service connection. Veterans do not have to prove that their current medical condition is related to their military service -- the law presumes it. Diseases that have a presumed service connection include chronic illnesses, tropical illnesses, tuberculosis, multiple sclerosis, and Hansen's disease, provided that they cause the veteran to be 10% disabled or more. If the veteran was a prisoner of war during active service and developed a disease or disability with a 10% or greater rating, diseases such as anxiety, post-traumatic osteoarthritis, residual frostbite, to name a few conditions, would be presumed service-connected. If that person was a prisoner of war for thirty or more days, disabilities to a 10% degree or greater including malnutrition, chronic dysentery, and liver cirrhosis (among many others) would be regarded as service-connected, and that veteran would be entitled to disability benefits. Certain forms of cancer are also presumed to be service-connected in cases where the veteran was subjected to radiation as part of their active military service (such as exposure to nuclear testing or explosion), and the veteran would therefore be eligible for disability benefits.
Pre-Existing Injury Aggravated by Military Service. In this type of service connection, the veteran had a condition prior to military service, and then an event occurred in military service that made the pre-existing condition worse. Example: a veteran had a skin condition prior to entering military service, but due to exposure to certain chemicals in the military, the skin condition was made worse than it ever would have been on its own. In situations such as this, the military service is said to "aggravate" the pre-existing condition. In such cases, the pre-existing condition usually must be noted on the service member's original medical exam, showing that the service member was not originally of sound health.
Secondary Service Connection. This type of service connection exists when one service-connected disability is the cause of another disability. The second disability does not need to be directly related to military service, but would not have occurred but for the first disability (the one caused by military service). A famous case of this type is of a WWII veteran who was treated for tuberculosis using medicine known to cause hearing loss. The hearing loss was not directly related to service, but it wouldn't have occurred if it weren't for the tuberculosis, which was service-connected. A present-day example is Diabetes Type II. When Diabetes Type II is service-connected, conditions such as peripheral neuropathy should be given serious consideration for secondary service connection.
Service Connection due to Injury Caused by Treatment in the VA Health Care System. If a veteran is injured because of VA hospitalization, treatment, rehab or therapy, the injury is automatically treated as service-connected (38 U.S.C. 1151).
If you are unsure if you disability will be considered service-connected, you may want to talk to a veterans disability attorney.