Unexpected medical care spending imposes considerable financial risk on developing country households. Based on managed care models of health insurance in wealthy countries, Colombia's Régimen Subsidiado is a publicly financed insurance program targeted to the poor, aiming both to provide risk protection and to promote allocative efficiency in the use of medical care. Using a "fuzzy" regression discontinuity design, we find that the program has shielded the poor from some financial risk while increasing the use of traditionally under-utilized preventive services - with measurable health gains.