Purpose: This study aimed to examine the relationship between the physical design of mental health care facilities and the occurrence of aggressive behaviour. Methods: A cross-national survey including a large number of forensic and non-forensic inpatient wards (n = 101) across seven National Health Service (NHS) trusts was conducted. A detailed Ward Features Checklist was designed and completed for each ward. These ward features were then compared on two dimensions with records of aggressive incidents on the wards. Clinical ward staff on participating wards (n = 191) also completed an online survey including questions from the Work Safety Scale (WSS) to assess subjective perceptions of safety at work. Results: Physical aggression was associated with higher staffing and greater space availability (Ward Features Checklist Dimension 1: Incident Rate Ratio = 2.19); and increased comfort and facilities and external views of urban environments (Ward Features Checklist Dimension 2: Incident Rate Ratio = 1.24). Conclusion: The findings here are amongst the first to challenge ideas about the relationship between staff-patient ratios, certain space characteristics and aggressive incidents. The observed associations are, however, underpinned by complex organisational and relational factors which need to be further explored to fully understand the overall context. There are implications for service user and staff safety training initiatives and for future mental health ward design.