Abstract: This retrospective quasi-experimental study reviewed assaults in two adult mental health inpatient rehabilitation units. The majority of clients in this area experience enduring mental health illnesses and have complex physical health issues. The service comprises of an intensive rehabilitation unit and a secure extended rehabilitation unit. Between May and August 2001 the service moved to purpose built facilities. The opportunity was taken to review clients' assaultive behaviour in the new environment and to compare the incidents with those in the old environment to see if there had been any significant changes. Data on assault incidents including time of assault, place of assault, who was involved and what preventative actions were suggested were collected from the Incident and Accident Hazard Reports (IAHR) dating from 1 April 2000 until 31 May 2002. Staff were expected to complete IAHR reports on all assault incidents. The research examined whether the change in environmental conditions impacted on clients' wellbeing in relation to assaultive behaviour. Trends within the IAHR reports were also examined in order to compare these to similar studies completed in other parts of the world. There were 141 IAHR reports of assault incidents. Fifty of these occurred in the pre move period, 38 in the transition phase and 53 in the post move. There was no significant difference in the rate of assaults in the pre-move to post move period. Completion of the IAHR forms was seen to be very problematic, especially in relation to legal status of perpetrators and documentation of prevention strategies. An urgent audit of existing practice is now required to establish if problems found with the quality and completion of the IAHR forms continues to be evident in the rehabilitation service and if present staff education is needed to improve the standard of documentation. Research is also needed to establish the extent to which staff implement strategies to prevent assaults, and to reduce recidivism.