Physical conditions of prisons have been at the center of long-standing debates in correctional policy and research. Many argue prisons should be unpleasant to deter future offending and motivate prosocial change among inmates. Others believe harsh conditions inhibit effective treatment and, perhaps, make offenders worse. Little progress in these debates has emerged, primarily because few studies exist that have tested propositions coming from either camp. This study draws on survey data collected from a random sample of staff at each of the 114 Federal prisons operating in 2007. Staff perceptions of noise, clutter, dilapidation, and privacy were combined to reflect physical conditions of each prison (aggregated to the prison level). Operational data measuring serious violence was used to create a count of serious assaults at each prison over the same time period referenced in the staff survey. Utilizing a Poisson framework, the data showed that poor physical conditions of prisons correspond to significantly higher rates of serious violence. Implications for theory and policy are discussed. Abstract published by arrangement with Sage Journals.