Cancer patients may be particularly vulnerable to errors due to the complex, multidisciplinary nature of the care they require and the risks of the treatments they must undergo. This qualitative study of patients undergoing treatment for breast or colon cancer found that a significant proportion of patients perceived they had experienced a preventable adverse event, most commonly ascribed to poor communication or coordination of care. Most patients did not report their concerns to clinicians and did not feel that errors were fully disclosed. The accompanying editorial calls for clinicians to communicate more effectively with patients throughout their course of treatment and followup. Efforts are also underway to engage patients in safety by providing training in reporting errors and patient–provider communication.