The benefits of cancer screening programmes accrue to those who have cancer or identifiable precancerous conditions, and in whom the disease progression is slowed or halted by earlier intervention. The costs accrue to the rest of the population for whom there is no direct benefit to health. Attention has been given to the medical risks of screening procedures and to the economic costs, but there has been very little regard paid to the psychological costs. The aim of this paper is to evaluate the psychological impact of screening. Screening participants who are found to have untreatable disease, or for whom the interventions prove ineffective, have a greater proportion of their life as a cancer patient with all the associated psychological (and perhaps physical) distress, but no increase in their life expectancy. Those who receive false positive results may experience acute psychological distress produced by the prospect of a grave diagnosis before they are found to be free from serious disease. Even the procedure of screening itself, with the disturbance of the invitation, the discomfort of the tests and the wait for the diagnosis, can have a significant impact upon some patients. This paper evaluates the psychological costs which may be involved across the whole screening procedure, from the possible alarm of receiving an invitation to participate in screening, to the trauma of a cancer diagnosis for someone who had been unaware of any symptoms.