Attention Deficit Hyperactivity Disorder (ADHD) is the most common neurodevelopment disorder among children and teens. ADHD used to be called Attention Deficit Disorder (ADD) but this is now outdated terminology.  ADHD is very common.  It is estimated that ADHD affects about 3.4% of children worldwide.  However the prevalence ranges across studies anywhere from 2-18% depending on the population