The relationship between anxiety and affective disorders continues to be debated in the literature. The authors report a case of identical twins concordant for attention deficit disorder and somnambulism but discordant for major depression and agoraphobia with panic attacks. The authors discuss the implications of this "finding in nature." Results from neuroendocrinological, family, and twin studies are also reviewed that either lend support or question the existence of a relationship between anxiety disorders and affective disorders.