Objective: There is growing emphasis on assessment of functional impairment for diagnosing psychological disorders and making disability/accommodation judgments. Focus to date has been on self-reported functional impairment, which, like self-reported symptoms, is likely vulnerable to malingering. We examined whether a highly recommended self-report measure of functional status (World Health Organization Disability Assessment Scale; WHODAS) is vulnerable to malingered Attention Deficit Hyperactivity Disorder (ADHD). Method: Using archived clinical data from undergraduate students referred for ADHD evaluation, we examined the relationship of the WHODAS to behavioral malingering (identified by Word Memory Test and embedded indicators) and to noncredible self-report (identified by validity scales of Minnesota Multiphasic Personality Inventory-2 Restructured Format; MMPI2RF) and an embedded measure on the Connors Adult Attention Rating Scale (CAARS). Results: Clinic referrals who showed signs of behavioral malingering scored significantly higher on WHODAS scales of Understanding and Communicating, Household Activities, and Participation in Society (all p < .05) relative to those who showed no signs of behavioral malingering. With regard to noncredible self-report, all WHODAS subscales were consistently correlated with Infrequent Responses, Infrequent-Psychopathology, and Response Bias Scale of the MMPI2RF (all p < .05, most p < .01), and many were correlated with the embedded CAARS validity measure as well. In addition, referrals whose MMPI2RFs were invalid scored significantly higher on several WHODAS subscales (p < .05 or greater) relative to those whose MMPI2RF profiles were valid. Conclusion: Results clearly demonstrate the vulnerability of self-reported functional impairment/disability to malingering and noncredible report, reminding clinicians of the need to assess malingering and noncredible report before interpreting self-report of functional limitations as accurate.