Iran hostage crisis, in U.S. history, events following the seizure of the American embassy in Tehran by Iranian students on Nov. 4, 1979. The overthrow of Muhammad Reza Shah Pahlevi of Iran by an Islamic revolutionary government earlier in the year had led to a steady deterioration in Iran-U.S. relations. In response to the exiled shah's admission (Sept., 1979) to the United States for medical treatment, a crowd of about 500 seized the embassy. Of the approximately 90 people inside the embassy, 52 remained in captivity until the end of the crisis.