This article looks at Eleanor Roosevelt's role within the intense debate on nuclear fallout as it developed in the US in the early 1950s. In particular, the article analyzes Mrs. Roosevelt's position on nuclear weapons, deterrence, and disarmament; her condemnation of nuclear testing; and her role as both a public intellectual and a mass educator who helped people to understand the real consequences of nuclear fallout. Here, Mrs. Roosevelt emerges as an active voice that, by defending freedom of speech, also contributed to popularizing the issue of nuclear fallout and making American citizens aware of the urgency of a ban on nuclear testing.