Despite evidence about the negative effects of verbal aggression in mental health wards there is little research about its prevalence or about the factors that predict the behaviour among inpatients. This study aimed to determine the prevalence of verbal aggression in a secure mental health service, and to examine the relationship of verbal aggression with risk factors for aggression in the risk assessment tool HCR-20 in order to establish whether, and with which factors, the behaviour can be predicted. Verbal aggression was measured using the Overt Aggression Scale (OAS) over a 3-month period across a heterogeneous patient group (n = 613). Over half the patients (n = 341, 56%) engaged in 1594 incidents of verbal aggression. The HCR-20 total, clinical, and risk management subscale scores predicted verbal aggression, though effect sizes were not large. Item-outcome analysis revealed that impulsivity, negative attitudes, and non-compliance with medication were the best predictors of verbal aggression and, therefore, should be targeted for intervention. There are key synergies between factors predicting verbal aggression and the core mental health nursing role. Nurses, therefore, are in a prime position to develop and implement interventions that may reduce verbal aggression in mental health inpatients.