People with Asperger's Syndrome typically are very interested in specific subjects and like to learn lots of details about them. They can become obsessed with in obscure subjects and enjoy talking in great detail about them, taking them very seriously. People with ADHD are likely to have lots of interests and to be less obsessive about following through on them. Both can have issues with social situations, with the people with Asperger's syndrome being unaware that people find them boring and struggling to understand why others aren't fascinated by their subject, while the people with ADHD may not notice what's going on around them and may be socially inappropriate, but they understand it when it is pointed out to them.
Asperger's Syndrome can be misdiagnosed as ADHD because of similar symptoms. In addition, ADHD and Asperger's Syndrome can occur together.
Some Comparisons:
ADHD - has difficulty focusing on one thing
AS - can focus very intently on one thing if it is a special interest but could have difficulty if it is not a special interest
ADHD - has difficulty completing tasks
AS - does not have difficulty completing tasks if it is a special interest
ADHD - might not seem to be listening when someone is speaking to him or her
AS - might not seem to be listening when intently focused or when overwhelmed
ADHD - talks nonstop
AS - talks nonstop about a special interest but often very little on other topics
ADHD - makes inappropriate comments due to being impulsive but realizes afterward it was inappropriate
AS - makes inappropriate comments due to not knowing better and not understanding social conventions
ADHD - shows emotions without restraint
AS - shows emotions when overwhelmed and stressed, but might seem unemotional at other times
ADHD - interrupts due to being impulsive
AS - could interrupt due to lack of understanding of social conventions but might not talk at all
ADHD - fidgets, squirms, moves constantly due to hyperactivity
AS - fidgets and squirms in some situations that can be resolved with a "fidget" that helps him or her focus or being put in a low-distraction low-stress environment
ADHD - has difficulty performing silent tasks
AS - usually does not have difficulty performing silent tasks if in low-distraction low-stress environment; can play quietly alone in a room
ADHD - has difficulty paying attention
AS - might have difficulty paying attention if subject is not a special interest or if person uses slang and idiomatic expressions that are not understood or if not in a low-distraction low-stress environment
ADHD - daydreams frequently
AS - daydreaming is not typically a symptom noticed in younger children, but it might be more common in girls and older children or teens
ADHD - forgets details of daily routines
AS - follows daily routines rigidly
ADHD - might have accidents and injuries due to being impulsive
AS - might have accidents and injuries due to lack of motor control