Psychiatric disorders are often associated with disturbed sleep. Poor sleep can attenuate emotional control, including the regulation of aggression, and thus, may increase the risk of impulsive, aggressive acts. This cross-sectional study aimed to investigate the potential contribution of sleep problems to subjective and objective aggressiveness and impulsivity in a forensic psychiatric population. Questionnaires on sleep quality (Pittsburgh Sleep Quality Index), chronic severe insomnia (Sleep Diagnosis List), aggressiveness (Aggression Questionnaire) and impulsivity (Barratt Impulsiveness Scale-11) were completed by 96 forensic psychiatric inpatients, admitted to two forensic facilities in the Netherlands. To obtain more objective measurements of aggression and impulsivity, observational scores on a professional instrument to assess the risk of future aggression (Historical Clinical Future-30) and reported aggressive incidents were collected from files. Results showed that a worse sleep quality and higher insomnia scores were significantly associated with self-reported aggression and impulsivity, clinician-rated hostility and involvement in aggressive incidents within the facility. Whether a participant was professionally judged as impulsive could not be predicted by sleep quality or the insomnia score. To a large extent the results of this study support the hypothesis that poor sleep is related to impulsive, aggressive behavior in forensic psychiatric patients. It is worthwhile to examine the protective effect of treatment of sleep difficulties on aggressive reactivity in (forensic) psychiatric populations. (C) 2013 Elsevier Inc. All rights reserved.