Objective Neuropsychological deficits are of major importance in ADHD, yet no previous studies have assessed clinically referred samples of older adults. The authors compared older adults with ADHD (60–75 years) with both younger adults with ADHD (18–45 years) and older healthy controls with regard to various neuropsychological deficits. Methods Well-established tests were used to investigate working memory, inhibition, switching, planning, fluency, and speed of processing. Self-ratings of executive functioning and delay-related behaviors were also included. Both variable-oriented and person-oriented analyses were conducted. Results Older adults with ADHD differed from controls with regard to working memory, inhibition, switching, and delay-related behaviors. In comparison to younger adults with ADHD, they performed at a similar level with regard to working memory and planning, but significantly better with regard to inhibition, switching, fluency, speed of processing, and delay aversion. Despite several significant group differences relative to controls, person-oriented analyses demonstrated that a majority of older adults with ADHD performed within the average range on each test and 20% showed no clear deficit within any neuropsychological domain. Conclusions The results are in line with models of heterogeneity that have identified different neuropsychological subtypes in ADHD as well as a subgroup of patients without any clear neuropsychological deficits. For older adults with ADHD, it will be important to assess their functioning across time as normal aging is related to memory decline and these patients could therefore end up with severe deficits as they grow older, which in turn could have serious negative effects on daily life functioning.