Bipolar disorder was once thought to occur only rarely in youth, with the peak age of onset in the early thirties.  However, approximately 20% of all bipolar patients have their first episode during adolescence, with a peak age of onset between 15 and 19 years of age.  Rates of bipolar disorder in children, once considered extremely low, are now thought to be closer to rates in adults, although due to questions of diagnostic reliability, true rates are not known.  It is known that 20% to 30% of youth with major depression go on to develop bipolar disorder.  The DSM-IV-TR criteria for bipolar disorder are not believed to adequately describe the symptoms present in childhood, which is why the disorder is often missed in the younger age groups.  Depression as well was once believed to be rare in children, but symptoms of major depression are now known to occur.  Rates of mood disorders in general in children have been rising over the past half-century for unclear reasons.  Bipolar illness in childhood is more likely to affect the offspring of parents with bipolar disorder.  While manic symptoms are the same in children as described for adults, the duration criteria are believed to be too long for diagnosis in children.  The mood shifts between mania, depression, and euthymia can occur several times whithin a day.  In addition, children with mania are more likely to be more irritable than elated.  Older bipolar adolescents are more likely to have presentations similar to adults.  In children, it may be difficult to distinguish bipolar disorder from attention-deficit hyperactivity disorder, oppositional-defiant disorder, conduct disorder, developmental disorders, or anxiety disorders.  Although there remains debate and controversy over the diagnoses of mania in children, it is increasingly recognized that there are children with severe affective dysregulation manifested by severe tantrums, destructiveness, and aggression that may in fact be early bipolar disorder.  In fact, childhood onset mania is often considered more chronic rather than episodic, most likely with a mixed (with depression) presentation and psychotic features more common.  Early-onset substance abuse may signal bipolar disorder as well.