Much discussion of the management of patients with cancer centers on what to tell the patient about his diagnosis. The more basic issue of what the patient already knows has not often been considered. Fifty patients were interviewed by a psychiatrist as they registered for treatment at the Radiotherapy Center of the Mount Sinai Hospital in New York. All had cancer. Forty (80 per cent) correctly gave their own diagnosis. These 40 patients were not told of their diagnosis by their physicians. How they learned they had cancer and how they reacted to that knowledge was the focus of this study. The degree of anxiety and depression in these patients was the basis for discussion of what helped them to function. A series of mechanisms of defense was found to be in use. None of these patients had attempted suicide, despite knowledge that they had cancer. The interrelationship of neuroses existing prior to the diagnosis of cancer, with emotional reactions to that diagnosis, was noted in 7 patients. Only 1 subject developed a new neurosis in response to learning the diagnosis of cancer. The physician's importance to the cancer patient was made clear by the patients in this study. An approach to understanding the patients' needs and the physician's opportunities to meet them, but also his difficulties in doing so, is the concluding section of this report.