This review aimed to assist clinicians in the identification and assessment of adult attention-deficit hyperactivity disorder (ADHD) with an emphasis on diagnostic and rating instruments. Pubmed and RISS were utilized to identify relevant studies and critical reviews on the diagnosis and assessment of adult ADHD, published between 1988 and 2010. The Adult ADHD Self-Report Scale-v1.1, the ADHD Rating Scale-IV, the Conners Adult ADHD Rating Scale, and the Current Symptoms Scale have been utilized for self-reporting of current ADHD symptoms. The Brown ADD Rating Scale, the ADHD Rating Scale-IV, the Current Symptoms Scale, and the Conners Adult ADHD Rating Scale have also been evaluated by an observer. The Childhood Symptom Scale and the Wender-Utah Rating Scale have been used for retrospective assessment of childhood ADHD symptoms and the Adult ADHD Investigator Symptom Rating Scale, the Adult Interview, the Brown ADD Diagnostic Form, the Conners adult ADHD diagnostic interview for DSM-IV, and the Wender-Reimherr Interview have been available as comprehensive diagnostic interviews. There is a wide variety of instruments available with respect to adult ADHD. The choice of appropriate instruments is essential for achieving accurate diagnosis and assessment of this disorder.