The purpose of this article is to explore assaultive behavior of psychiatric in-patients in a hospital and to examine the interplay of patient, environmental, and staff factors related to assault. The present study was carried out prospectively using standardized instruments applied in four acute wards in one hospital. A log system was used to record the occurrence of assaults. The results showed 595 episodes of assault from 238 patients in 7 months. Forty one nurses participated in the study. To further examine the differences between assaultive and non-assaultive patients, and assaulted and non-assaulted nurses, a logistic regression analysis was used. The results indicated that patient factors (diagnosis, history of assault, time since admission, and history of smoking), environmental factors (patient/nurse ratio and spatial density), and staff factors (age, length of work experience, training program received in prevention and management of assaults) are contributing variables to assaultive behavior. The present study examined a wider range of variables than have been included in many previous studies. This reinforces the necessary complexity of models likely to prove useful in predicting assaults among psychiatric inpatients.