Providing a cost of diagnosis for attention deficit hyperactivity (ADHD) would be next to impossible. The amount really depends on who is diagnosing you (family practitioner, psychiatrist, psychologist, social worker, etc.) and whether you have neuropsychological testing or not. The cost could run from a few hundred to several thousand dollars. Most public mental health clinics have staff that can diagnose but the waiting time for an appointments is usually several months.