Involuntary autobiographical memories are memories of personal events that come to mind with no preceding retrieval attempts. They have been studied broadly in autobiographical memory for decades and shown to be common and mostly positive in everyday life. Clinical literature has focused on negative intrusive memories of stressful events and tended to neglect other forms of involuntary autobiographical memories. However, recently, there has been an upsurge of research addressing involuntary memories more broadly in clinical disorders, including both stressful and mundane memories, and both real life events and simulated events. We here provide the first integrated and comprehensive review of all studied types of involuntary memories in clinical and subclinical populations. We review their frequencies and characteristics across a broad selection of memory properties. A systematic search of the PsycInfo, PubMed, and Web of Science databases yielded 79 empirical studies, with the majority focusing on depression, post-traumatic stress disorder, and psychosis, and a few addressing attention-deficit/hyperactivity disorder, bipolar disorder, eating disorders, health anxiety, obsessive-compulsive disorder, and social anxiety. Findings show that an increased frequency of involuntary memories-in all forms-is found across disorders, possibly reflecting executive deficits. Additionally, heightened negativity, greater emotional impact, and the use of maladaptive emotion regulation strategies in response to these memories are typically reported among individuals with PTSD and depression, but less consistently for psychotic disorders. Overall, the findings identify involuntary memories with distinct characteristics as a transdiagnostic phenomenon, suggesting a deeper understanding of mental health problems and more targeted treatment approaches.