Violent and aggressive behaviour is a serious problem among hospitalised psychiatric patients. The aim of this study was to assess factors that may help predict violent behaviour in psychiatric inpatients. Method: The study group consisted of 107 patients hospitalised in the Department of Adult Psychiatry, Poznan University of Medical Sciences in Poznań, with a diagnosis of bipolar disorder (n = 58), schizophrenia (n = 39) and anxiety disorders (n = 10). Sociodemographic and clinical data were obtained through a review of medical records and patient interviews using a self-prepared questionnaire. Results: Of 107 respondents, aggressive behaviour occurred in 46 patients (42.99%). A low risk of aggressive behaviour was observed in 68 patients (63.6%), medium risk – in 37 patients (34.6%), and high risk – in 2 subjects (1.9%). The study demonstrated a significant association between aggressive behaviour and short duration of the illness (p = 0.002), the criminal history of the patient (p = 0.003), the use of sedatives (p = 0.04), unemployment (p = 0.00034) and male gender in patients with a diagnosis of bipolar disorder (p = 0.03). There were no statistically significant differences between the incidence of violence and the main diagnosis (p = 0.56). The study showed no association with alcohol (p = 0.5) and psychoactive substance abuse (p = 0.07), age (p = 0.8), addiction in family (p = 0.1), history of suicide attempt (p = 0.08) and the lack of insight into the illness (p = 0.8). Conclusions: Based on these results, it appears that the most important factors in the occurrence of aggressive behaviour were criminal history, prior violent behaviour and short duration of the illness. The use of sedative drugs and male gender were also significant risk factors.