Bipolar disorder is an affective disorder defined on the basis of the presence of periods of elevated mood. Patients often present with depression, and previous episodes of elevated mood may be missed if not specifically explored during assessment. Bipolar disorder may be difficult to differentiate from other conditions causing mood instability and impulsivity. It is important to identify comorbidities such as substance use, neurodiversity and physical illnesses. The first-line treatment for mania is antipsychotic medication. Antidepressants are reported to have little to no efficacy in treating bipolar depression on average. Lithium is not the only long-term prophylactic agent, but it remains the gold standard, with good evidence that it reduces mood episodes and adverse outcomes. Monitoring is required to ensure lithium level is optimised and potential side-effects minimised.