To investigate the overlap between dissociative and bipolar disorders with reference to their neurophysiological foundations. Case reports of anomalous lateralization and shifts in handedness associated with both affective and dissociative conditions have intermittently surfaced in the literature. The two disorders are, however, usually considered to be distinct psychopathological entities. A case of co-occurring bipolar disorder and dissociative identity disorder (DID) is presented. The "switch" in personality coincided with manic or hypomanic symptoms and was associated with a change in handedness. A parallel between the "personality" shifts that characterize DID and the mood fluctuations that underlie bipolar disorder is drawn, suggesting some nosological overlap between the two disorders. The possibility that these two psychiatric conditions share a similar neurophysiological architecture is also raised.