Manic-depressive (bipolar) disorder is a severe, relapsing mental illness that shares characterstics both with major depressive disorder and with serious mental illnesses such as schizophrenia. Like schizophrenia, it is a chronic disorder, and is treated primarily in the specialty mental health sector. Rates of appropriate treatment are low. Functional outcome is compromised for the majority of individuals who have this disorder. Societal costs are exceeded only by those for schizophrenia. Existing cost calculations likely underestimate societal costs because of underestimating functional impact and neglecting to account for the substantial proportion of individuals who are institutionalized outside of the health care system (e.g., in prison). Little is known as yet regarding manic-depressive disorder in historically underserved groups and in vulnerable groups such as the elderly. There are major lacunae with regard to this disorder in the grant portfolios of all federal agencies mandated to address the needs of Americans with serious mental illnesses. The authors in the context of the Wider NIMH Affective Disorders Workgroup propose several specific recommendations to address the needs of this costly and underresearched disorder.