"Congress has maintained an interest in the effects of gang violence in Central America, and on the expanding activities of transnational gangs with ties to that region operating in the United States. The violent Mara Salvatrucha (MS-13) and its main rival, the '18th Street' gang (also known as M-18) continue to threaten citizen security and challenge government authority in Central America. Gang-related violence has been particularly acute in Honduras, El Salvador, and Guatemala, which have among the highest homicide rates in the world. In recent years, governments in those countries appeared to move away, at least on a rhetorical level, from repressive anti-gang strategies. However, continuing gang-related violence prompted El Salvador to adopt tough new legislation on gangs in September 2010. Guatemala may follow suit. U.S. officials have expressed concerns about the expanding presence of the MS-13 and M-18 in cities across the United States, as well as reports that these gangs may be evolving into more sophisticated transnational criminal enterprises. Between February 2005 and October 2010, U.S. officials arrested some 3,332 alleged MS-13 members in cities across the United States, many of whom were subsequently deported. Evidence suggests, however, that previously deported members of both the MS-13 and the M-18 often reenter the United States illegally."
CRS Report for Congress, RL34112