Using a survey applied to incarcerated populations in Latin American countries, this study aims to examine the factors that determine the existence of violence in prisons and explain why some penitentiaries are more violent than others by studying variables such as inmate age, sentence length, and crime type. A quantitative examination is used to determine the effect of these variables on prison violence (property theft and beatings), and whether it is a result of the living conditions within the prisons. The results indicate that the most overpopulated prisons, with the worst living conditions, have the lowest levels of violence (in Brazil and El Salvador). The lower rates of violence observed in certain Latin American prisons appear to be explained by the existence of criminal governments within penitentiary systems, organized and run by a dominant prison gang.