More than 15 years have passed since the terrorist attacks of 11 September 2001, and a comprehensive re-examination of the 9/11 attackers is now warranted. Research on the psychology of terrorists has evolved dramatically, and there is also new information on some offenders. The present study provides the available psychological and psychiatric evidence on each of the 9/11 pilots, muscle hijackers, and thwarted hijackers who intended to participate in the "planes operation." Overall, findings suggest that the 9/11 terrorists may have had significantly more mental health problems than previously assumed, and the leaders who planned 9/11 personally approved suicide attackers with prior histories of mental illness. By widely publicizing this information, security officials may be able to more effectively delegitimize suicide terrorism and reduce the number of individuals who would consider funding, supporting, or committing these deadly attacks.