Most experts in the field believe that ADD has a strong component related to inheritance. So you will often find one or both parents with some variation of ADD. However, since ADD is usually related to some kind of brain physiology problem, it can also come from birth trauma or early head injury. These latter two scenarios are somewhat less likely.
Another way to look at where ADD comes from is that it has to do with the way the brain is functioning. Recent electrophysiological studies have found that about 95% of the time, the truly ADD person has one of five types of brain waves patterns, according to Quantitative Electroencephalogram (QEEG) studies. Even though there may be a definable brain physiology with most ADD people, there is a tendency for people to inherit their parents' brains. But in the lives of most parents of present day adults, ADD was not well known. Therefore, the parents had no perspective on the likelihood that their child had this disorder. As a result, the parents probably behaved towards their children in an "ordinary" way, disciplining the child for the distractibility as if it could be changed at will. But with the truly ADD child, such training at home and at school may have had little effect. What resulted, far too many times, was a low self-esteem.
Might you have a Learning Disability? Many of you might not know exactly what a learning disability is. When adults first come to me, even those who definitely know they have a learning disability, I ask them what they think a learning disability is. Sometimes they think that the person is slow in all areas, or even that the learning disabled person is retarded. The simple answer of what a learning disability is that the person has some learning function (like reading) which scores lower than their overall intelligence. So, an average intelligence person might read very slowly. Or a very bright person reads merely in the average range.
Have you had a Head Injury? If you have had a head injury, you may experience symptoms similar to ADD. Technically, such a person might not qualify for ADD because this injury was not something you were born with. It is also sometimes possible people do not connect their head injury with the symptoms associated with ADD, and so go from therapist to therapist, doctor to doctor, without getting the right treatment. Diagnosis and treatment of a head injury is similar to the procedures of dealing with learning disabilities, so much of the discussions found in this site may apply.