Bipolar disorder (BD) usually onset during adolescence but can also be present in prepubertal children. The symptoms of BD in youth are similar to those in adults, but given the psychosocial developmental stage of the child, the presence of comorbid disorders, and the high prevalence of subsyndromal and mixed and rapid cycling presentations, the differential diagnosis of BD among youth can be challenging. Early-onset BD is associated with poor prognosis and high risk for suicidality, substance abuse, poor psychosocial functioning (e.g., academic, work, and relationships with family and friends), physical/sexual abuse, legal problems, and medical complications. Most initial presentations are depressive episodes, and after the initial mania/hypomania episode, up to 80% recover. However, of those who recover, in a period of 2 months–12 years, about 80% will have at least one recurrence, and 60% will have two or more recurrences. Recurrences are mainly depressive episodes followed by mixed presentations. Some factors, such as the presence of comorbid disorders, history of abuse, less time in remission, and parental psychopathology, are associated with greater risk for recurrences. The course of BD in youth is heterogeneous; however, a risk calculator (RC) was developed to predict risk for recurrences with high accuracy and then externally validated. Moreover, an RC was also developed and externally validated to predict the individual risk for suicide attempts. A substantial group of youth has BD-not otherwise specified (NOS) mainly because they do not have the Diagnostical and Statistical Manual of Mental Disorders (DSM), which requires a 4- to 7-day duration of symptoms to be diagnosed with BD-I/II. This group of youth demonstrates similar psychopathology, risk for suicidality and substance abuse, family history of BD, and genetic profile as youth with BD-I/II, and up to 50% eventually will convert into BD-I/II. The most potent factor that increases the risk of developing BD is a family history of BD, especially if the parents’ BD onset came early in life. This, combined with ongoing anxiety, depression, mood lability, and subsyndromal manic symptoms, may increase the child’s risk of developing BD by up to 50%. These prevalence rates are for the group, but a recent RC showed good accuracy in predicting the risk of developing BD for a particular individual. The presence of a high BD polygenic risk score significantly enhanced the accuracy of the RC. The early identification and appropriate treatment of BD in youth is crucial given the deleterious effects of this illness on the psychosocial development of the child and the increased risk for suicidality. Some of these factors associated with risk for onset and recurrence are amenable to change and support the importance of delivering evidence-based interventions for youth and their family members. Hopefully, in the future, reliable and valid biological and behavioral markers will be identified to help diagnose BD, predict the prognosis, and guide treatment options.