A large body of research has focused on indicators of the risk of prison violence, especially in the United States. Little is known about this question in Spain, despite the fact that in 2010, this country had the most crowded prison system in western Europe. This prospective study draws on official data to examine the relationship between individual and situational characteristics and misconduct in a sample of 1,330 inmates from 11 penitentiary facilities across a 10-month period. Violent misconduct was less frequent than potentially violent behavior, with prevalence rates of 9% and 13%, respectively. Younger age, being on remand, classification as first degree, prior violent behavior, drug and/or alcohol problems, poor response to treatment, and procriminal attitudes were significant risk factors of inmate misbehavior in an ordinal regression model (areas under the curve = 0.74 to 0.82). Having a violent conviction offense was not a significant predictor of outcome. The implications for current classification practices are discussed, and the importance of cross-cultural and empirically based research is stressed.