Recent research has demonstrated that attention-deficit/hyperactivity disorder (ADHD), one of the most common mental disorders in childhood, continues into adulthood. In adulthood, however, pharmacotherapy with psychostimulants still is an off-label treatment. Because of this we routinely administer a test dose of methylphenidate (MPH) prior to a continuous medication and measure MPH effects quantitatively and repeatedly employing a neuropsychological test battery. To probe if the acute effects of MPH are indeed helpful in predicting longer-term efficacy of MPH treatment we retrospectively analyzed the neuropsychological test results of 34 patients on continuous MPH medication. Two testing sessions had been performed without MPH (at baseline and 24 h after a single dose intake to control possible training effects), one after a single dose and one after 3-6 months of regular intake of MPH. A significant improvement of performance in tests assessing attentional, memory and executive functions after single medication was maintained on long term medication in those 23 patients available for follow-up. These results indicate that beneficial short term effects of MPH predict longer-term effects and may thus be helpful in the decision for an off-label treatment. Controlled prospective studies are now necessary.