Bipolar disorder is a severe psychiatric disorder, characterized by depressive, manic and mixed episodes. The illness affects about 1-2 % of the population. Bipolar I disorders affect both genders equally, whereas bipolar II disorders seem to occur more frequently in women. The classification of the different subtypes of bipolar disorders is done depending on the severity and frequency of the episodes. Other subtypes beside bipolar I and bipolar II disorder are rapid cycling (more than 4 episodes of mania, depression, hypomania or mixed state in one year) and cyclothymia (hypomanic and subdepressive symptoms over a two year period). Besides a thorough psychiatric and neurological examination, further clinical tests should be performed in order to exclude differential diagnosis (psychiatric as well as neurological and somatic diseases). The course of the illness is often negatively affected by the high frequency of psychiatric and somatic comorbidities. After all the prognosis of bipolar disorder is depending on the individual course of the illness. Notably comorbidities and psychotic symptoms seem to have a negative influence on the prognosis.