Self-harm refers to the purposeful destruction of bodily tissue without suicidal intention and for purposes that are not socially sanctioned. Little is known about the associations between a history of self-harm, mood symptoms, and functioning in adults with different types of mood disorders. Lifetime histories of self-harm, current mood symptoms, global functioning, and affective traits were collected on 142 adults with mood disorders. The prevalence of lifetime self-harm was higher in patients with bipolar disorder compared with patients with a unipolar depressive disorder. Self-harm was also more strongly linked to impulsivity in individuals with bipolar disorder compared with unipolar depressive disorder. Across both diagnoses, histories of self-harm were related to lower levels of current global functioning, more severe depressive symptoms, and high self-reported emotional dysregulation and neuroticism. Findings indicate that self-harm is a potent prognostic variable for symptoms, global functioning, and personality functioning in individuals with mood disorders.