Havana syndrome is a disputed medical condition reported primarily by U.S. diplomatic, intelligence, and military officials stationed in overseas locations. Most of the affected individuals reported an acute onset of symptoms associated with a perceived localised loud sound, followed by chronic symptoms that lasted for months, such as balance and cognitive problems, insomnia, and headaches. The first cases were reported by U.S. and Canadian embassy staff in Havana, Cuba, though earlier incidents may have occurred in Frankfurt, Germany. Starting in 2016 through to 2021, several hundred U.S. intelligence and military officials and their families reported having symptoms in overseas locations including China, India, Europe, Hanoi, as well as in Washington, D.C., USA.