The ability to treat many types of cancer with oral chemotherapy has benefited patients by minimizing hospitalizations, but it also places the burden to avoid medication errors on them as they must administer risky medications correctly. Prior studies have shown that adults and children with cancer are particularly vulnerable to medication errors and that most oncology practices do not have specific safeguards in place to improve oral chemotherapy medication safety. This study used direct observation (during home visits) to determine the epidemiology of medication errors among children with cancer and found a staggeringly high incidence of 36 potentially harmful errors per 100 patients—higher than some studies of hospitalized patients. The authors judged that more than one-third of the errors could have been prevented by better communication between patients and physicians.