More than 1 in 10 children has been diagnosed with it, according to the Centers for Disease Control and Prevention, which surveyed more than 95,000 parents in 2011.
ADHD diagnoses have been rising since at least 1997, according to CDC data. Experts think that's because more doctors are looking for ADHD, and more parents know about it.
The condition makes it hard for kids to pay attention and control impulsive behaviours. It's often treated with drugs, behavioural therapy, or both.
The latest survey found about 11 per cent of children ages 4 through 17 had been diagnosed with ADHD. That translates to nearly 6 1/2 million children. Half of children are diagnosed by age 6, the study found.
A 2007 survey put ADHD diagnoses at 9.5 per cent of kids.
The CDC survey asked parents if a health care provider told them their child had ADHD. It's not known how thorough the assessment was to reach that conclusion.
ADHD diagnoses were increasing at a rate of about 6 per cent a year in the mid-2000s, but slowed to 4 per cent a year from 2007 to 2011. That may reflect that doctors are closer to diagnosing most of the kids with the condition, said the CDC's Susanna Visser, the study's lead author.