Studies investigating sleep and personality disorders consistently demonstrate a relation between personality disorders characterized by behavioral disinhibition and/or emotional dysregulation (traditionally termed cluster B personality disorders) and poor sleep. This finding is in line with previous studies associating insomnia with impulsive behavior, since this is a core characteristic of both antisocial and borderline personality disorder. The current study investigates a group (n = 112) of forensic psychiatric inpatients with antisocial or borderline personality disorder or traits thereof. Subjective sleep characteristics and impulsivity were assessed with the Pittsburgh Sleep Quality Index, the Sleep Diagnosis List, and the Barratt Impulsiveness Scale, respectively. More than half of the patients (53.6%) report poor sleep quality and 22.3% appears to suffer from severe chronic insomnia. Both poor sleep quality and chronic insomnia are significantly associated with self-reported impulsivity, in particular with attentional impulsiveness. This association was not significantly influenced by comorbid disorders. Actively treating sleep problems in these patients may not only improve sleep quality, mental health, and physical well-being, but may also have impact on impulsivityrelated health risks by increasing self-control.