Attention deficit hyperactivity disorder (ADHD) often persists into adulthood. Stimulant drugs, including methylphenidate, have showed efficacy in trials for ADHD in adults. Adult psychiatrists are likely to encounter increasing numbers of adult patients who may benefit from methylphenidate. A systematic review of the literature was made to examine the evidence on the safety of methylphenidate, when used therapeutically in adults. Twenty-six placebo-controlled trials were found, in which 811 adults received methylphenidate for ADHD and other conditions. In the short term, methylphenidate was well tolerated and no serious side effects were observed. There is little information on the long-term safety of methylphenidate in adults, although the number of serious adverse effects reported to regulatory authorities has, so far, been low. Methylphenidate is associated with a modest rise in blood pressure and heart rate. Surveys of stimulant use in US universities show that misuse of prescribed medication, for recreation or to enhance study, is fairly common although the level of harm that arises from this practice is unclear.