Cotard's syndrome is a rare psychiatric disorder characterized by nihilistic delusions in which the patient is convinced that death has occurred or the internal organs have perished. The treatment of Cotard's syndrome requires monotherapy or combination therapy with antidepressants, antipsychotics, mood-stabilizing drugs or electroconvulsive treatment (ECT). We describe a woman with severe depression and Cotard's syndrome who responded well to ECT. This case is not only an example of a patient with Cotard's syndrome, but also an example of how quickly and severely a delirium can develop.