Most studies dealing with the familiality and genetics of mood disorders have been limited to adults, but several studies suggest that there is continuity between childhood- and adolescence-onset depression and mania and adult illness. More direct estimates of the heritability of depressive symptoms or episodes in children and adolescents indicate that the genetic contributions may be greater than 50%. A number of functional and structural imaging studies have identified particular circuitry as being involved in the generation of emotion and mood disorders. Imaging studies of twins have suggested that regional brain volume and characteristics of brain shape are heritable. A potentially important new avenue of research will be the correlation of the genetics of brain structure or function with the genetics of mood disorders. Preliminary studies of adolescent and young adult twins suggest a significant correspondence between the genetic contributions to some regional brain volumes and early-onset mood disorders.