There are a lot of complicated and complex studies about what causes ADHD, and a lot of folk lore and popular theories.

There are also some basic facts about what does appear to cause ADHD and what doesn't.

Environmental factors: It appears that tobacco and alcohol use by expectant mothers can cause a higher risk of ADHD in offspring. There is also evidence that high levels of lead may be related to ADHD in children.

Brain injury: One early theory was that attention disorders were caused by brain injury. Some children who have suffered accidents leading to brain injury may show some signs of behavior similar to that of ADHD, but only a small percentage of children with ADHD have been found ot have suffered a traumatic brain injury.

Food additives and sugar: While it is popular to think sugar causes or exacerbates ADHD, this does not seem to be true. In 1982, the National Institutes of Health held a scientific consensus conference on this issue and found that diet restrictions helped about 5 percent of children with ADHD, mostly young children who had food allergies.

Genetics: ADHD runs in family, so there are likely to be genetic influences, but no one knows exactly what those are.

In short, no one really knows what causes ADHD most of the time, but there are some factors, such as prenatal alcohol and tobacco consumption and genetic predisposition, that seem to increase a child's likelihood of having ADHD.

Information from this article comes from the National Institute of Mental Health Report "Attention Deficit Hyperactivity Disorder."