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.