It has often been claimed that aircraft hijacking is a "contagious" phenomenon, that the motivation to hijack aircraft spreads from one individual to another as a result of media coverage of hijacking incidents. This article develops a mathematical model of contagion and applies it to aircraft hijackings in the United States between 1968 and 1972. Analyses show that successful hijackings in the United States did generate additional hijacking attempts of the same type (either transportation or extortion). There were no contagion effects of unsuccessful hijacking attempts in the United States or any effects on U.S. hijacking attempts of such attempts outside the United States.