ment to heightened creativity during hypomanic episodes may contribute to ambivalence
about seeking treatment or undermine adherence to treatment. 
Prevalence
The 12-month prevalence of bipolar II disord er, internationally, is  0.3%. In the United
States, 12-month prevalence is 0.8%. The prevalence rate of pediatric bipolar II disorder is
difficult to establish. DSM-IV bipolar I, bipola r II, and bipolar disorder not otherwise spec-
ified yield a combined prevalence rate of 1. 8% in U.S. and non-U.S. community samples,
with higher rates (2.7% inclusive) in youths age 12 years or older. 
Development and Course
Although bipolar II disorder can begin in late adolescence and throughout adulthood, av-
erage age at onset is the mid-20s, which is slight ly later than for bipolar I disorder but ear-
lier than for major depressive  disorder. The illness most of ten begins with a depressive
episode and is not recognized as bipolar II d isorder until a hypomanic episode occurs; this
happens in about 12% of individuals with the initial diagnosis of major depressive disor-
der. Anxiety, substance use, or eating diso rders may also precede the diagnosis, compli-
cating its detection. Many individuals expe rience several episodes of major depression
prior to the first recognized hypomanic episode. 
The number of lifetime episodes (both hypomanic and major depressive episodes)
tends to be higher for bipolar II disorder than for major depressive disorder or bipolar I
disorder. However, individuals with bipolar I disorder are actually more likely to experi-
ence hypomanic symptoms than  are individuals with bipolar II disorder.The interval
between mood episodes in the co urse of bipolar II disorder tends to decrease as the indi-