Fundación Misión Medica El Salvador (FMMES) is the sister organization to Medical Mission International. MMES was organized under the non-profit laws of El Salvador and, as a Salvadoran NGO, it is the organization that operates the David V. King Medical Center.

FMMES is also involved in fund-raising activities within El Salvador both in coordination with MMI and to fund its own expenses. They are also working to establish long-term relationships and programs to help ensure the long-term sustainability of the center.