Maladaptive daydreaming (MD) is the excessive employment of immersive daydreaming characterized by highly absorbing fantasy experiences that become a preferred focus of consciousness at the expense of living in the real world. Active dissociative processes like depersonalization and derealization, including those also characteristic of dissociative identity disorder (DID): amnesia, identity confusion, and identity alteration, may be present and, like in DID, seem to be psychodynamically driven. Comorbidity with attention deficit disorder, obsessive-compulsive disorder, post-traumatic stress disorder, and others is typical. Often associated with profound shame experience, it is, like DID, a condition that tends to be concealed and requires a clinician to be knowledgeable about its nature before a diagnosis can occur and effective treatment be initiated. We introduce the concept, explore its clinical associations and manifestations, and provide several case vignettes to illustrate the breadth and depth of this potentially debilitating variation on daydreaming.