This paper considers the likelihood that precision-guided munitions (PGMs) in the hands of terrorists will be used against civilian aircraft, both fixed and rotary winged, with attendant casualties. The author concludes that the most likely threat is the shoulder-fired surface-to-air-missile (SAM). Historically, such munitions have been used routinely on a world-wide basis at the rate of several per year for the last 15 years with considerable success. Countermeasures against what is currently in the field and available to terrorists are inadequate. In addition, SAM of more advanced design are being developed and will likely be available on the open market. Current countermeasure approaches, already insufficient, will be completely outclassed by advanced SAM designs.