Covert antisocial behaviors such as stealing, destroying property, and cheating carry high risk for delinquency. An individual laboratory setting was devised in which youngsters could take desired objects and use answer keys to assist with worksheets. Twenty-two boys with attention-deficit hyperactivity disorder (ADHD) and 22 comparison boys were observed on two occasions, with the ADHD Ss receiving a methylphenidate-placebo crossover. Laboratory stealing and property destruction were positively correlated with maternal and staff ratings of parallel behaviors. Methylphenidate resulted in significant reductions of these acts, but it also effected an increase in cheating, presumably because of its enhancement of task involvement. The generalizability of the laboratory findings, actions of stimulants in this domain, and the ethics of experimental investigations of covert antisocial behavior are discussed.