This paper examines the causal impact of inflows of internal displaced people (IDP) on homicides in Colombian host municipalities during the period 1999 to 2014. A priori, the authors suggest that IDP inflows might increase crime because: (a) IDPs were exposed to violence and research indicates that this can engender violent behaviors; (b) l IDPs lack economic opportunities; (c) IDPs tend to be younger, are more likely to be male and have low levels of education; and (d) IDP inflows reduce unskilled wages and increase low-income rentals in host cities, and to the extent that this affects economic conditions, it may be expected that criminality increases for both IDPs and non-IDPs. Using an instrumental variables approach (to address the potential endogeneity of the location choices of IDP), the authors find that there is a sizable impact of IDP inflows on criminality. A standard deviation increase in IDP inflows, increases the homicides rate by 0.6 standard deviations. This effect is larger in cities and among men. The results are mostly explained by homicides of permanent residents in the municipalities. While IDP inflows are associated with increasing homicide rates for all age groups, the effects are larger for young individuals (15-19 and 20-24 years old). The impact of IDP inflows on homicides is short lived, lasting at most 5 quarters.