Psychological stress has been claimed to contribute to the onset of cancer and to increase mortality from a number of non-malignant diseases. We investigated the effect of a genuine psychological stressor, i.e. cancer in a child, on the incidence of cancer and mortality from non-malignant 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 1943-85; their parents were identified from population registers. Overall, 1665 parental malignancies were diagnosed from the date the cancer of the child was reported until 1992, compared with 1702 expected from national incidence rates, yielding 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 statistically significant deviation of the relative risk from unity was seen for any period of follow-up after the stressful event, and no excess risk was seen for any particular type of cancer. Moreover, a total of 2137 parental deaths were observed over the period 1974-92, compared with 2333 expected from national mortality rates, giving an overall standardized mortality ratio of 0.9 (range 0.9-1.0). 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 non-malignant diseases. We conclude that the human organism is highly adaptable, even to extreme psychological stress.