Researchers of the gifted have traditionally advanced the theory, though they are often without data to support it, that an association between intellectual and/or creative giftedness and mood disorders exists. This assumed association is often referred to as the "mad genius theory." This article explores the origins and development of the theory and describes the difficulties that arise when evaluating it due to problems associated with defining and measuring the relevant terms. Finally, the article examines the current scientific knowledge concerning the association between mood disorders and intellectual and/or creative giftedness. Broadly speaking, the data support the association as it relates to the construct of creativity and mood disorders and as it relates to the relationship between high IQ and bipolar disorder but not high IQ and depression. (Contains 2 notes.)