This study with 107 male forensic patients with developmental disabilities investigated whether exposure to parental anger and aggression was related to anger and assaultiveness in a hospital, controlling for background variables. Patient anger and aggression were assessed by self-report, staff-ratings, and archival records. Exposure to parental anger/aggression, assessed by a clinical interview, was significantly related to patient self-reported anger, staff-rated anger and aggression, and physical assaults in hospital, controlling for age, intelligence quotient, length of hospital stay, violent offense history, and childhood physical abuse. Results are consonant with previous findings concerning detrimental effects of witnessing parental violence and with the theory on acquisition of cognitive scripts for aggression. Implications for clinical assessment and cognitive restructuring in anger treatment are discussed.