Attention-deficit/hyperactivity disorder (ADHD), the most common neurobehavioural disorder and amyotrophic lateral sclerosis (ALS), the most common adult motoneuron disease, may be two distinct entities on first sight. This paper aims to highlight parallels concerning clinical features and neurobiology. The presence of increased physical and psychological activity and largely non-progressive frontal dysfunction associated with impaired executive control and decreased attention are characteristic clinical features of both, ADHD and ALS. At the neurobiological level, there is evidence for hyperactivity in the glutamatergic system and a - potentially related - dopaminergic hypoactivity in ADHD and ALS. The clinical features of ALS resembling ADHD are particularly characteristic for the premorbid stage of the patient. Therefore, we hypothesize that clinical features of ADHD may be a risk factor for the development of ALS. This hypothesis is currently of unknown pathogenetic, but of potential future therapeutic relevance. Our hypothesis of a link between ADHD and ALS could also be considered as an example how research on neurodevelopmental diseases might influence the understanding and possibly the prevention and treatment of neurodegenerative diseases.