130 Bipolar and Related Disorders
Prevalence
The 12-month prevalence estimate in the contin ental United States was 0.6% for bipolar I
disorder as defined in DSM-IV. Twelve-month prevalence of bipolar I disorder across 11
countries ranged from 0.0% to 0.6%. The life time male-to-female prevalence ratio is ap-
proximately 1.1:1. 
Development and Course
Mean age at onset of the first manic, hypomanic, or major depressive episode is approxi-
mately 18 years for bipola r I disorder. Special considerations are necessary to detect the di-
agnosis in children. Since children of the same chronological age may be at different
developmental stages, it is difficult to defi ne with precision what is “normal” or “ex-
pected” at any given point. Therefore, each ch ild should be judged according to his or her
own baseline. Onset occurs throughout the life  cycle, including firs t onsets in the 60s or
70s. Onset of manic symptoms (e.g., sexual or so cial disinhibition) in late mid-life or late-
life should prompt consideratio n of medical conditions (e.g., frontotemporal neurocogni-
tive disorder) and of substance ingestion or withdrawal. 
More than 90% of individuals who have a sin gle manic episode go on to have recurrent
mood episodes. Approximately 60% of manic episodes occur immediately before a major
depressive episode. Individuals with bipolar I disorder who have multiple (four or more)
mood episodes (major depressi ve, manic, or hypomanic) within 1 year receive the speci-
fier “with rapid cycling.” 
Risk and Prognostic Factors