Behavior and symptoms seen in 48 24-h periods preceding violent episodes and 93 control observations were studied. Six behaviors were more common before violence: confusion, irritability, boisterousness, physical threats, verbal threats and attacks on objects. A logistic regression equation based on these behaviors in a randomized half of the observations predicted the occurrence of subsequent violence in 92.1% of the other half of the sample without any false positives, giving a sensitivity of 81.3% and a specificity of 100%. It is concluded that mentally ill people display the same behaviour before violent acts as we would expect in people without such disorder. The potential for short-term prediction of violence seems good.