Prevention of medication errors has long been a concern of pharmacists in all practice settings, including specialty treatment and research centers. Oncology pharmacists have always been particularly aware of this concern because many of the cytotoxic drug therapy regimens we use are already at the maximum tolerated doses, thus leaving no margin for error. During the past 10 years, catastrophic chemotherapy medication errors have occurred in some of the finest hospitals and cancer centers in the United States, bringing unprecedented public and governmental awareness of the risk of such errors. In addition, the March 2000 report by the Institute of Medicine of the National Academy of Sciences, To Err Is Human: Building a Safer Health System, has prompted legislative and executive branch reaction at the federal level aimed toward reducing medical errors of all types, including medication errors.The purpose of this article is to review the types and causes of catastrophic chemotherapy medication errors that have occurred in oncology and to discuss tools and methods aimed at improving the safety of medication use, particularly chemotherapy, in the United States.