ADHD is not typically diagnosed until school-age, but there is growing recognition that symptoms often emerge by the preschool years. There is also some evidence that symptoms may begin even earlier during the toddler years, but little is known about how common ADHD symptoms are during toddlerhood and whether they can be distinguished from normative toddler behavior. Our lab is examining the validity of ADHD symptoms in 2-year-old children, including an examination of the factor structure at this age as well as the relation between symptoms and temperament. We are also examining the stability of the symptoms from age 2 to age 4.