Many insurgent groups operate across international borders, but transnational insurgent activities are seldom observable and little is known about their consequences. In this paper I show that activity by Colombian insurgent group FARC increased disproportionately in Colombian municipalities next to the border with Venezuela after Hugo Chávez became president of the latter. I argue that FARC's reliance on short-range weaponry and non-mechanized transportation limited the area in which the group could expand its operations as a result of access to a cross-border safe haven. In consequence, the finding above constitutes evidence of increased FARC presence in Venezuela during the Chávez administration. Exploiting the plausibly exogenous change of government in Venezuela, I find that Colombian municipalities more exposed to a cross-border guerrilla sanctuary experience large increases in the intensity of violence, as well as reductions in local tax revenue and educational enrolment.