This talk will consider some of the more serious risks that have resulted from problems with human-computer interfaces, and assess the role of the HCI relative to the other risks that must be considered. There are many cases in the RISKS archives in which the HCI has been implicated, such as the Aegis shootdown of the Iranian Airbus, the Stark defense against Iraqi Exocets, the Discovery laser experiment over Mona Kea, various modern aircraft accidents, an F-18 missile that was launched while still clamped to the aircraft, various commercial aircraft and air-traffic-control problems, train accidents, Three Mile Island, the Therac 25 radiation device, heart monitors and pacemakers, medical-care systems, and all sorts of security problems and name or identifier confusions, to name just a few. A few paradigmatic cases will be considered, and some recommendations discussed.