In May 2000, a passenger with measles traveled aboard a 7-hour flight from Japan to Hawaii. A follow-up survey was sent to 307 (91%) of the 336 exposed passengers to identify susceptible passengers and subsequent occurrences of measles. The median age of the 276 respondents (90%) was 34 years; 268 (97%) were residents of Japan. Self-reports determined that 173 (63%) were immune through prior measles or vaccination; 6 (2%) denied a history of prior measles or immunization, and 97 (35%) were unaware of their status. Only 1 nonimmune respondent received immunoprophylaxis. None of the respondents developed a febrile rash illness 7-21 days after exposure. The risk of in-flight measles transmission among passenger populations with similar susceptibility profiles appears to be low. An aggressive response by health departments may not be warranted after airborne exposure to measles. Each health department should make such determinations on the basis of specific circumstances and availability of resources.