Background. Identify a group of adults with ‘undiagnosed’ attention deficit hyperactivity disorder (ADHD) and compare their personal and family medical histories, psychosocial profiles, functional impairment and quality of life with non-ADHD controls. Additionally, compare adults with undiagnosed and diagnosed ADHD to investigate possible reasons why the undiagnosed avoid clinical detection.

Method. ICD-9 codes for ADHD in administrative claims records and responses to a telephone-administered adult ADHD screener [the Adult ADHD Self-Report Scale (ASRS)] were used to classify approximately 21000 members of two large managed health-care plans as ‘undiagnosed’ (no coded diagnosis; ASRS positive) or ‘non-ADHD’ controls (no coded diagnosis; ASRS negative). Patients identified as ‘undiagnosed’ ADHD were compared with samples of non-ADHD controls and ‘diagnosed’ ADHD patients (ICD-9 coded ADHD diagnoses) on the basis of demographics, socio-economic status, past and present mental health conditions, and self-reported functional and psychosocial impairment and quality of life.

Results. A total of 752 ‘undiagnosed’ ADHD subjects, 199 ‘non-ADHD’ controls and 198 ‘diagnosed’ ADHD subjects completed a telephone interview. Overall, the ‘undiagnosed’ ADHD cohort demonstrated higher rates of co-morbid illness and greater functional impairment than ‘non-ADHD’ controls, including significantly higher rates of current depression, and problem drinking, lower educational attainment, and greater emotional and interpersonal difficulties. ‘Undiagnosed’ ADHD subjects reported a different racial composition and lower educational attainment than ‘diagnosed’ ADHD subjects.

Conclusion. Individuals with ‘undiagnosed’ ADHD manifest significantly greater functional and psychosocial impairment than those screening negative for the disorder, suggesting that ADHD poses a serious burden to adults even when clinically unrecognized.