Psychiatric disorders are associated with autonomic dys-regulations. There is evidence that these dys-regulations are partly responsible for the increased mortality in patients with psychiatric disorders. The determination of the heart rate variability (HRV) is a method easily applicable and allows the assessment of the autonomic control of the heart rate regulation. A multitude of HRV parameters with different physiological meanings have been introduced, the most widely used parameters are presented and characterized in this paper. Many studies have shown a reduced HRV in patients with major depression. Most studies found a reduced parasympathetic activity. However some authors discuss an elevated sympathetic activity. The magnitude of HRV reduction correlates to the severity of the depression. In patients with coronary diseases, major depression is an independent risk factor of mortality. Antidepressive therapy with serotonin reuptake inhibitors has failed to improve the prognosis of this patients. Patients with panic disorders also have a reduced HRV due to an elevated sympathetic control and reduced vagal control. In schizophrenic patients a reduced HRV was found in long term electrocardiogram recordings, whereas short term recordings did not show a reduced HRV. Patients with Alzheimer's disease also have a reduced HRV, which is limited to the low frequency component. Therapy with cholinesterase inhibitors further influences HRV by reducing the high frequency component and might increase the risk for arrhythmias. HRV analysis and integration in the assessment and monitoring of psychiatric patients before and during therapy elucidate the role of autonomic disturbances in such diseases and may help to optimize treatment.