Chronic administration of the amphetamine-derivative methylphenidate (MPH) may induce appetite reduction and weight loss. By contrast, the effects that stopping chronic MPH may exert on eating behavior and body weight are poorly known. We report the case of a male patient with childhood attention deficit/hyperactivity disorder (ADHD), who discontinued MPH treatment at the age of 11 years and was lost to follow-up until the age of 16. The patient's body mass index increased by five points within 1 year of MPH cessation while the symptoms of ADHD were re-emerging. The patient secondarily developed DSM-5 criteria for eating disorders. Discontinuing chronic MPH can significantly affect weight and eating behavior. Such risks should warrant further studies, as they could be particularly increased in patients with ADHD, who share common vulnerability factors with both obesity and eating disorders.