Since Ritalin (methylphenidate immediate-release or MPH IR) was first marketed in 1955, it has been a mainstay of treatment for Attention-Deficit/Hyperactivity Disorder (ADHD). The postulated mechanism of action, adverse events and efficacy of MPH are examined. MPH formulations that are currently on the market in the United States and those that will soon be available are considered. Various products are examined by comparing onset of effect and duration of action. MPH has a well-known efficacy and safety profile. The development of extended-release (MPH-ER) was a significant advance in ADHD treatment. Recent products offer convenience in terms of dosing and timing of drug administration to improve symptom control, but efficacy is similar among all MPH-ER products. One formulation may be more appropriate for an individual patient, but no product offers significant advantages over all others. Since MPH is only effective in about 80% of patients, identifying factors that predict drug response is an active area of research. Although MPH is not effective for every patient, until there is a better understanding of the genetic contributions and nuances of functioning of central nervous system pathways, MPH will be a first choice for the treatment of ADHD.