Attention deficit hyperactivity disorder (ADHD) in adults is associated with significant social, legal, occupational, and psychiatric difficulties. The estimated prevalence of ADHD in the adult population is between 0.3% and 5%. Recent interest in the condition in adults has been accompanied by the appearance of a number of readily available scales for screening adults and aiding in the diagnosis of ADHD in this age group. However, there are few published data on the validity and reliability of such measures. We examined the diagnostic and screening utility of three ADHD scales (Adult Rating Scale [ARS], Attention-Deficit Scales for Adults [ADSA], and Symptom Inventory for ADHD) in 82 adults presenting for ADHD evaluation. All three instruments were sensitive to the presence of symptoms in adults with ADHD (correctly identifying 78% to 92% of patients with ADHD), but a high proportion of individuals with non-ADHD diagnoses screened positive (incorrectly identifying between 36% and 67% of non-ADHD patients). Our results suggest that the use of such measures for screening and as an aid in diagnosis should be approached with considerable caution.