Attention deficit hyperactivity disorder (ADHD) is a condition that affects people's behaviour. Children with ADHD can seem restless, may have trouble concentrating and may act on impulse.
Symptoms of ADHD tend to be noticed at an early age and may become more noticeable when a child's circumstances change, such as when they start school.
Most cases are diagnosed when children are under 12 years old, but sometimes it's diagnosed later in childhood.
Sometimes ADHD was not recognised when someone was a child, and they are diagnosed later as an adult.
The symptoms of ADHD may improve with age, but many adults who were diagnosed with the condition at a young age continue to experience problems.
People with ADHD may also have additional problems, such as sleep and anxiety disorders.