Professionals working in the public sector in the UK report widespread violence towards staff working in areas such as health care, social services and education. This study compares the characteristics of patients with and without a history of violence in a large sample of patients attending a community mental health service in South East England. The data were taken from a study of comorbidity and cannabis use in a mental health trust covering a semi-rural population of 250 000 people in Harlow and the surrounding area of South East England. Key workers were interviewed using semi-structured questionnaires from the Comorbidity of Substance Misuse and Mental illness in Community Mental Health and Substance Misuse Services study. Rates of violence against health workers were more than 20 times higher among those patients with a history of violence (23.6% vs. 1%, P < 0.001). Alcohol and drug use was more frequent in those who were violent. Prevalence of comorbidity, schizophrenia and personality disorders was high. Key workers' estimates suggested that there was no difference in aggression, engagement or adherence to care plan among those with a history of violence.