The first of a series of meetings, sponsored by Physicians for Social Responsibility, took place in Cambridge, Massachusetts, in February 1980, to consider the Medical Consequences of Nuclear Weapons and Nuclear War. It was followed by others elsewhere and led to the horrifying convictions that (1) it is highly unlikely that any nuclear war would be ‘limited’, and (2) no effective medical response can be conceived to deal with the human damage which would result from a nuclear attack. Consequently an organization entitled International Physicians for the Prevention of Nuclear War has been established to hold further meetings and promote general enlightenment towards avoiding widespread—even global—human carnage and environmental destruction which would accompany a nuclear war involving even a small fraction of the weapons that now exist.The atomic bomb which was exploded over Hiroshima in August 1945 is estimated to have killed 75,000 of that city's population of 245,000 and to have destroyed two-thirds of the 90,000 buildings within the city limits. It had an explosive power equivalent to 20,000 tons of TNT, whereas many of the thermonuclear devices now deployed at the ready are some 50 times more powerful than it although still far less destructive than the most devastating contemporary weapons. Consequently the world's leaders must be brought to their senses and these horrific weapons dismantled to avoid what could be ‘the last epidemic’.The magnitude of the problem can be gauged from the fact that at present more than 50,000 nuclear warheads are reported to be deployed and ready to launch—most of them being sufficient in destructive power to dwarf the bomb that was used against Hiroshima. Sufficient nuclear devices exist outside the United States to destroy totally every major American city. Six nations are now acknowledged possessors of nuclear weapons, and there are almost certainly others to increase the degree of instability. This situation is not so much ‘unthinkable’ as insufficiently realized or even thought about—hence the failure to reject nuclear war as a ‘viable option’ in the conduct of world affairs. Medically, any treatment programmes would be virtually useless and the costs quite staggering, so prevention becomes imperative.