Comorbidity in bipolar disorder is the rule rather than the exception more than 60% of bipolar patients have a comorbid diagnosis and is associated with a mixed affective or dysphoric state; high rates of suicidality; less favourable response to lithium and poorer overall outcome. There is convincing evidence that rates of substance use and anxiety disorders are higher among patients with bipolar disorder compared to their rates in the general population. The interaction between anxiety disorders and substance use goes both ways: patients with bipolar disorder have a higher rate of substance use and anxiety disorder, and vice versa. Bipolar disorder is also associated with borderline personality disorder and ADHD, and to a lesser extent with weight gain. As more than 40% of bipolar patients have anxiety disorder, it is indicated that while diagnosing bipolar patients, systematic enquiry about different anxiety disorders is called for. This also presents a therapeutic challenge, since agents that effectively treat anxiety disorders are associated with the risk of induced mania. Therefore, the treating psychiatrist needs to carefully evaluate the potential benefit of treating the anxiety against the potential cost of inducing a manic episode. A possible solution would be to use, when possible, a non-pharmacological intervention, such as a cognitivebehavioural approach. Alternately, it is suggested that the clinician attempts to ensure that the patient receives adequate treatment with mood stabilizers before slowly and carefully attempting the addition of anti-anxiety compounds with a relatively lower risk of mania induction (e.g. SSRIs compared to TCAs).