The September 11 terrorist attacks demonstrated that the technical competence, available resources, level of preparation and suicidal determination of contemporary terrorist groups like al Qaeda have greatly increased over the last decade. This article will consider the likelihood that sophisticated terrorist groups could successfully launch sabotage attacks against nuclear research reactors and cause radiological releases that threaten nearby populated neighborhoods. While the theft by terrorists of highly enriched uranium (HEU) from research reactors to make relatively simple gun-type nuclear explosives has been a concern for some time, the sabotage threat to research reactors—a threat which is independent of fuel enrichment—has not been widely addressed. Nuclear regulators should reassess the level of physical protection that research reactor operators provide in light of the increased terrorist threat.