Australian-born American physician and activist whose advocacy focused on the medical and environmental hazards of nuclear weapons.

Helen Broinowski graduated in 1961 from the University of Adelaide Medical School with Bachelor of Medicine and Bachelor of Surgery degrees (the equivalent of an American M.D.) and married William Caldicott, a physician, in 1962. She worked as a general practitioner and pediatric intern, then founded and directed a cystic fibrosis clinic at Queen Elizabeth Hospital in Adelaide.

Caldicott began her antinuclear activism in 1971 with a warning to the Australian public about the potential consequences of the French government's atmospheric testing of nuclear weapons in the South Pacific. Pointing out the extent to which radioactive fallout was already present in food and water, Caldicott enlisted scientists, newspaper editors, and the general public to oppose the tests through demonstrations and boycotts of French products. Such activities contributed to the 1972 electoral victory of the Labor Party, which opposed the testing. Caldicott's efforts to ban the Australian export of uranium were ultimately unsuccessful.

In 1975 Caldicott and her family moved to the United States; settling in Boston, she became an associate at Children's Hospital Medical Center and an instructor in pediatrics at Harvard Medical School (1977–80). There she published Nuclear Madness: What You Can Do! (1978; with Nancy Herrington and Nahum Stiskin), in which she explained the consequences of nuclear technology in vivid, accessible language. She also gave numerous public lectures and made television appearances.

In 1978 Caldicott revived an organization known as Physicians for Social Responsibility and redirected its focus to the health risks posed by nuclear power. She also founded a Washington, D.C., lobbying group, Women's Action for Nuclear Disarmament, in 1980.

Caldicott's views on the nuclear industry were featured in the 1982 film If You Love This Planet, which was produced by the National Film Board of Canada. Although it won an Academy Award, the U.S. Department of Justice declared the film political propaganda and monitored its distribution. In 1983 Caldicott resigned as president of Physicians for Social Responsibility, citing differences between her goals and those of the wider membership. She continued to lecture and write in opposition to nuclear arms, however.

In 1984 Caldicott published Missile Envy: The Arms Race and Nuclear War. A subsequent book, If You Love This Planet: A Plan to Heal the Earth (1992), addressed broader environmental issues. Her autobiography, A Desperate Passion, was published in 1996.