Medical errors are common, and physicians face increasing pressure to fully disclose unanticipated outcomes and medical errors to patients. From an ethical perspective, disclosure is the right thing to do and is wholly consistent with the fiduciary model of the asymmetric physician-patient relationship, in which the patient, vulnerable due to illness, places trust in the expertise and person of the physician. When medical errors occur, the physician-patient relationship is fundamentally tested, and when physicians fail to offer an apology or explanation, patients often perceive a violation not only of their safety, but also of their trust. The issue of which events merit disclosure is still under debate. The most widely disseminated disclosure standard, from the Joint Commission on Accreditation of Healthcare Organizations, requires that patients be informed about all outcomes of care including “unanticipated outcomes,” as defined in the current terminology (Table 1). Although many aspects of patient safety and disclosure are common to all fields of clinical medicine, errors and adverse events have important specialty-specific dimensions. Oncologists face unique challenges in caring for cancer patients that may contribute to the risk of medical errors and to the difficulty of disclosing them to patients. The complexity of most cancer treatments, involving the use of different antineoplastic agents along with concurrent medications and supportive therapies, can make it especially difficult for oncologists to determine whether an adverse event was a result of treatment toxicity, a treatment adverse effect that was more severe or different than expected, or the result of a medical error. The use of detailed chemotherapy protocols makes harmful errors less likely, whereas the need for multiple concomitant medications increases the possibility of their occurrence. In addition, the involvement of interdisciplinary teams in oncology patients’ care may increase the possibility of error or, conversely, may contribute to prevention or earlier detection of some errors. Finally, cancer patients may be enrolled onto clinical trials or may receive relatively new drugs for which adverse effects are not known fully. These factors can increase the odds of adverse events, if not errors. Although most physicians agree on the importance of telling the truth to their patients when a harmful error has occurred, recent studies reveal a gap between patients’ expectations that errors will be disclosed to them and actual clinical practice. Moreover, many unanswered questions remain about how to disclose errors and how disclosure affects liability, patient satisfaction, and other outcomes. In general, oncologists are accustomed to communicating bad news about prognosis and risks in the context of the physical and psychological suffering of cancer patients. This experience makes them natural leaders in the medical profession’s efforts to improve the disclosure of harmful medical errors to patients. This article reviews recent professional approaches to patient safety and the disclosure of medical errors, and addresses some critical aspects of patients’ and physicians’ responses to harmful errors in oncology. We explore different dimensions of disclosure and suggest possible future research, policy, and clinical interventions.