Significant left subclinical hemi-neglect or "hemi-unawareness" in juvenile and adult ADHD has been reported many times. However, this literature has never been thoroughly reviewed, and is generally ignored in neuropsychological accounts of ADHD. The purposes of the present report were (1) to introduce a systematic review of this literature and (2) to prospectively test whether adults with ADHD (combined type) would present left hemi-unawareness measurable on a test of executive function commonly used with children and adults with ADHD, the Colour-Word Interference Test of the Delis-Kaplan Executive Functions System. This test requires participants to discriminate unusual stimulus characteristics by stating words aloud while visually scanning plates comprising either 50 colour patches or 50 words. A total of 28 ADHD adults (combined type) and 30 IQ-, age-, and gender-matched controls completed the task. The ADHD group manifested a significantly higher proportion of errors on the left than right sides of the plates. This atypical left-right balance was related to severity of the ADHD according to the Conners' Adult ADHD Rating Scale (CAARS) as well as to several other indicators from the Continuous Performance Test-II.