THERE has been a recent increase in inquiries concerning the present practice of smallpox vaccination in the United States. This can be traced in part to the excellent studies of Dr. Henry Kempe who has made many contributions to knowledge of smallpox and vaccination and has called attention to the question—Is the risk of smallpox in the United States today sufficient to warrant the risk of the complications of smallpox vaccination? It is pertinent to examine the salient facts. THE BACKGROUND Before the days of widespread vaccination, smallpox was epidemic in most parts of the world, with a morbidity rate of 25% and a case fatality rate of 20 to 80%, averaging 50% for variola major. Successful vaccination was introduced over 160 years ago, but the disease still persists. In the past 12 years, reported cases in the world have fallen from 500,000 to 100,000; but it is certain that many cases are not reported. Smallpox is gone from North America, Europe, Russia, and Oceania but may be reintroduced by air travelers from endemic areas much more easily than in the past when intercontinental travel time was usually longer than the incubation period of smallpox. For example, smallpox was introduced into 18 countries by travelers in the year 1956. In 1962 there were 24 deaths among 60 cases stemming from imported cases in the United Kingdom. In Europe in 1963 five cases were imported and caused a total of 140 secondary cases with 11 deaths in Sweden, Poland, Germany, Hungary, and Switzerland.