Objective: This multicenter study estimated the prevalence of bipolar disorder (BPD) among emergency department (ED) patients in Latin America. Methods: To identify patients with BPD, a combination of DSM IV-criteria interview and the Mood Disorder Questionnaire (MDQ) was used. Data from 1,505 patients from hospitals in Argentina, Brazil, Chile, Colombia, and Mexico was analyzed. Results: The prevalence of BPD in this sample was 5.2% (95% CI = 4.5% to 6.9%). Themean age was 37 years (response rate of 83.0%). Compared to non-BPD patients, BPD patients were more likely to report asthma (16.7% vs. 9%), thyroid problems (12.8% vs. 5.8%), seizures (23.1% vs. 3.0%), obesity (39.7% vs. 26.9%), alcohol abuse (30.8% vs. 10.0%), attention deficit hyperactivity disorders (50.0% vs. 12.0%), depression (81.6% vs. 45.7%), obsessive compulsive disorder (20.1% vs. 3.0%), panic disorders (23.1% vs. 12.3%), phobic disorders (11.2% vs. 3.1%), and any anxiety disorder (82.1% vs. 41.8%; all p <= 0.05). Suicidal plans and attempts were also significant higher in the bipolar group (11.5% vs. 2.8% and 10.3% vs. 1.8% respectively). Multivariate analysis identified ADHD, depression, alcohol abuse, anxiety disorder, and last month suicide plans and attempts to be independently associated with BPD. Conclusion: Our study supports that BPD is prevalent in ED in Latin-American countries and that comorbidity is the rule, not the exception. Patients presenting at ED with irritability, anxiety, pressure speech, euphoria, with suicidal tendencies, involved in risky behaviors, alcohol abuse, dependence or those with history of mental health hospitalization in the past 12 months must be assessed for comorbid BPD. (Int'l. J. Psychiatry in Medicine 2011;42:49-67)