Attention-deficit hyperactivity disorder (ADHD) is increasingly recognized not only in children but also in adults. Neuropsychological tests are important tools to quantify the attentional and/or cognitive deficits of patients compared to controls. The present meta-analysis integrates 24 empirical studies reporting results of at least one of 50 standard neuropsychological tests comparing adult ADHD patients with controls. The 50 tests were categorized into the following 10 functional domains: verbal ability, figural problem solving, abstract problem solving, executive function, fluency, simple attention, sustained attention, focused attention, verbal memory, figural memory. For each domain a pooled effect size d′ was calculated. Complex attention variables and verbal memory discriminated best between ADHD patients and controls. Effect sizes for these domains were homogeneous and of moderate size (d′ between 0.5 and 0.6). In contrast to results reported in children, executive functions were not generally reduced in adult ADHD patients.