Three patients with lung cancer, a man aged 68, a woman aged 69 and a man aged 52, denied the nature or the severity of their disease in three different ways: temporary denial to evade acute emotional shock, full-blown persistent denial, and unjustified optimism respectively. The psychological mechanism of denial may become operational in patients confronted with an overwhelming disease. A less pronounced denial of medical information provided by physicians can be recognised in many patients. It may also be noticed in how individuals or groups of people sharing the same unbearable reality face up to the facts. Denial may be helpful in (temporarily) circumventing a serious problem but when the disease is serious, it may interfere in relationships with partners, relatives and friends. Denial must be differentiated from organicity, e.g. anosognosia in cerebral damage, by patient ignorance, or by vague communication from the medical community. A direct and blunt confrontation of denial may result in adverse effects due to a defensive mechanism being aggravated. Slowly providing the patient with pieces of information whilst taking into account his or her reaction, may provide a clue for gradual conformation to the medical reality.