Impulsivity can be defined as a tendency to react rapidly, little or no mature forethought and plan to a stimulus without the consideration of the possible negative consequences of these reactions. Impulsivity as a dimension has been studied in many different psychiatric disorders and there is a growing body of evidence in recent years. Among the various mood disorders, impulsivity was found to be particularly associated with bipolar disorders. Most of the studies indicated high levels of impulsivity during acute phase of illness and some in remission. For instance, siblings of bipolar patients showed higher impulsivity scores comparing with healthy controls that may be interpreted as an endophenotype and vulnerability marker for bipolar disorders. Some of the common clinical features of bipolar disorders were also found to be associated with impulsivity among patients with bipolar disorders such as suicidality, alcohol and/or substance use, anxiety, cigarette smoking, aggressive behaviors and criminality. However, it is still unclear whether impulsivity is a trait or state phenomenon in bipolar disorders. Lack of evidence on the etiology of bipolar disorders makes it difficult to answer this question. Nevertheless, the possible role of impulsivity on nature of the bipolar spectrum disorders is remarkable and should be investigated in future researches including genetic and neuroimaging techniques among bipolar patients, their unaffected siblings and healthy controls.