Idiopathic dilated cardiomyopathy (IDCM) is an often fatal heart disease characterized by ventricular dilation and reduced systolic function. Despite advances in diagnostic and therapeutic techniques that have enabled earlier identification of patients with IDCM, the etiology of the disease in most patients remains unknown. The current 5-year survival rate for patients with asymptomatic IDCM approaches 80%; this is a significant improvement compared with earlier reports of the natural history of IDCM. Men are more commonly afflicted with IDCM, but women with IDCM tend to present with more advanced disease. Recent analysis of 3-year transplant-free survival reveals no gender differences, however. Survival in children with IDCM is variable; 30% of infants die within 2 years of diagnosis, but 5-year survival for childhood IDCM is 60% to 84%. An association of IDCM with the peripartum period is well recognized. The etiology of peripartum cardiomyopathy remains unknown, and some cases are familial. This disease is reversible in approximately 50% of patients, and in patients with intractable congestive heart failure, cardiac transplantation is a viable treatment option. AIDS has been more recently associated with IDCM. Acute left ventricular dysfunction and consequent dilated cardiomyopathy occur with increased frequency in patients with advanced AIDS. The etiology of dilated cardiomyopathy in HIV-infected patients is presently poorly understood. Survival for patients with AIDS after development of left ventricular dysfunction is extremely poor.