Estimates as to the worldwide prevalence of bipolar disorder are mixed. It is thought there is a lifelong prevalence rate of about 0.3-1.5% internationally for bipolar disorder. According to Merikangas et al, using World Health Organization information, it's about 0.6% for bipolar I, 0.4% for bipolar II and about 1.4% subthreashold bipolar disorder.

Comparatively, in the United States, the lifelong prevalence for bipolar disorder is thought to be from 1-1.6%. This is broken down into 1% for bipolar I, 1.1% for bipolar II and about 2.4-4.7% subthreashold bipolar disorder. It is not known why bipolar disorder (especially subthreashold) appears more frequently in the United States.

References: Medscape Reference - http://emedicine.medscape.com/article/286342-overview#showall

Estimates as to the worldwide prevalence of bipolar disorder are mixed. It is thought there is a lifelong prevalence rate of about 0.3-1.5% internationally for bipolar disorder. According to Merikangas et al, using World Health Organization information, it's about 0.6% for bipolar I, 0.4% for bipolar II and about 1.4% subthreashold bipolar disorder.

Comparatively, in the United States, the lifelong prevalence for bipolar disorder is thought to be from 1-1.6%. This is broken down into 1% for bipolar I, 1.1% for bipolar II and about 2.4-4.7% subthreashold bipolar disorder. It is not known why bipolar disorder (especially subthreashold) appears more frequently in the United States.

References: Medscape Reference - http://emedicine.medscape.com/article/286342-overview#showall