Background : Bipolar disorders are mostly genetically determined brain disorders, but primary brain dysfunctions and damage to the brain may also provoke clinical features suggesting the presence of a bipolar disorder. Aims: To review our current knowledege about standard EEG and qEEG findings in patients with bipolar I and II disorders, and discuss the value of assessing EEG and qEEG in routine clinical assesment of patients with bipolar I and II disorders. Methods: A literature search was conducted (key words: bipolar disorder, manic depression, EEG, electroencephalography) in PsychInfo PsychInfo (149 articles), Medline Ovid (510 articles) and Pubmed (524 articles) and by browsing some key psychiatric journals (Am J Psychiatry, Arch Gen Psychiatry, Biol Psychiatry, Electroencephalography, Cinical Neurophysi, Epilepsy and Behavior , J Affective dis, J Neurol, Neurosurg Psychiatry). EEG abnormality was defined as interictal spike discharge or sharp waves, epilepsy or findings suggesting epileptic disturbance including TIRDA; IRDA and small sharp spike activity. Theta-activity was only counted as abnormal if the activity was described as unilateral focal slowing of physiological rhythms by 1 Hz or more, or was unilateral with loss of reactivity of a physiological rhythm (e.g. loss of reactivity of the alfa-rhythm to eye opening or mental alerting) occuring in an awake adult not using any drugs. Results: Most studies were more than five years old and of limited quality in particular when it came to neuropsychiatric assessments and control of psychiatric comorbidity known to influence EEG patterns.. Abnormal EEG was found in a subgroup of patients with bipolar I and II disorders. Abnormality was associated with negative family history of affective disorders; female gender and higher mean age.The findings regarding qEEG characteristics and bipolar disorder were less consistent. In general terms there was asymmetric activity in frontotemporal brain regions in patients with bipolar disorders. qEEG predicted treatment response in some studies. Interpretation: Currently regular EEG is most useful for identification of abnormal brain dysfunctions in the temporal and frontal brain areas underlying bipolar symptomatology. qEEG offers promising possibilities for predicting treatment response. However, interpretation of qEEG records are still cumbersome and time-consuming limiting its use as a clinical tool. There is a great need for better designed electrophysiological studies of bipolar disorders. Good studies may provide important clinical information for the treatment of bipolar disorders.