Psychological stress has been claimed to contribute to the onset of cancer and to increase mortality from a number of nonmalignant diseases. We investigated the effect of a genuine psychological stressor, i.e. cancer in a child, on the incidence of cancer and mortality from nonmalignant diseases of 11,231 parents in a Danish nationwide population-based study. The children were identified from records in the Danish Cancer Registry for the period 1943-1985; their parents were identified from population registers. Overall, 1665 parental malignancies were diagnosed from the date the cancer of the child was reported through 1992, as compared with 1702 expected from national incidence rates, to yield standardized incidence ratios of 1.0 (95% confidence interval, 0.9-1.0) for all parents, 1.0 for mothers and 1.0 for fathers. No excess mortality was seen from causes associated with allergic illness, autoimmune conditions, chronic illness or changes in behaviour. Our data provide no support for the hypothesis of an association between psychological stress and the incidence of cancer or mortality from nonmalignant diseases. We conclude that the human organism is highly adaptable, even to extreme psychological stress.