Oppositional Defiant Disorder - called ODD for short - is a childhood mental disorder characterized by a pattern of disobedient, hostile, and defiant behavior towards authority figures. To fit the diagnosis, the behavior must persist for at least six months and occur more often than might be expected for the child's age and developmental stage, as some oppositional behavior is to be expected as a child grows.
A child with ODD loses his temper easily and frequently, argues, is deliberately annoying, blames others for his mistakes, etc.
One study found that 20 percent of children with Oppositional Defiant Disorder were also diagnosed with bipolar disorder, while 45 percent of children with both ODD and Conduct Disorder also had bipolar disorder.
Also see Conduct Disorder
Greene, R.W., et al. "Psychiatric Comorbidity, Family Dysfunction, and Social Impairment in Referred Youth With Oppositional Defiant Disorder." Am J Psychiatry 159(2002): 1214-1224.