To provide a better estimate of the prevalence of ADHD in adulthood, the authors complete a telephone survey of 966 randomly selected adults. They compute two diagnoses from the survey data. Participants meeting "Diagnostic and Statistical Manual of Mental Disorders" (4th ed.) criteria for both childhood and adulthood are defined as narrow ADHD. Broad ADHD adds to that definition those meeting subthreshold criteria. Cronbach's alpha is 0.90 for the 18 "DSM-IV" symptoms in childhood and 0.88 when rated for current symptoms in adulthood. No one item unduly influences the reliability of the total score. The authors find similar results in separate analyses of hyperactive-impulsive and inattentive symptoms. They estimate prevalences of 2.9% for Narrow ADHD and 16.4% for Broad ADHD. Having ADHD is associated with lower levels of education and employment status. These findings suggest that adult ADHD is a common disorder associated with impaired functioning. (Contains 2 tables and 3 figures.)