Patients with Cushing's syndrome were studied (n = 209, 78% females). Control patients had pituitary adenomas secreting growth hormone or prolactin. Age at diagnosis of Cushing's syndrome was 8-74 (mean 39) years. Duration of symptoms was 0.2-9 (median 2.0) years. Adverse life events within the 2 years preceding the onset of Cushing's syndrome were not significantly commoner than in controls. Depressive illnesses were associated with the presence of adverse life events (p < 0.001). Depressive illness was more common in females (p < 0.01). There were no significant differences in the severity of depression in the different types of Cushing's syndrome. Pathological anxiety had been diagnosed in 26 patients (12%), mania or hypomania in six patients (3%) and confusion in three patients (1%). Psychotic illness had been diagnosed in 16 patients (8%) and was more common in adrenal carcinomas (p < 0.01). Significant psychiatric illness, usually depressive, preceded the onset of all symptoms and signs of Cushing's syndrome in 25 patients (12%); 23 of these developed pituitary Cushing's disease, and two adrenal adenomas. When Cushing's syndrome was diagnosed, significant psychiatric illness, usually depression, was present or had been a feature of Cushing's syndrome in 120 (57%) patients.