Secondhand smoke (SHS) exposure causes death and disease among nonsmoking adults and children. Adopting policies that completely prohibit smoking in all indoor areas is the only effective way to eliminate involuntary SHS exposure. Among the 29 large-hub U.S. airports, five currently allow smoking in specifically designated indoor areas accessible to the general public. In 2011, these five airports had a combined passenger boarding of approximately 110 million. To assess indoor air quality at the five large-hub U.S. airports with designated indoor smoking areas and compare it with the indoor air quality at four large-hub U.S. airports that prohibit smoking in all indoor areas, CDC measured the levels of respirable suspended particulates (RSPs), a marker for SHS. The results of this assessment determined that the average level of RSPs in the smoking-permitted areas of these five airports was 16 times the average level in nonsmoking areas (boarding gate seating sections) and 23 times the average level of RSPs in the smoke-free airports. The average RSP level in areas adjacent to the smoking-permitted areas was four times the average level in nonsmoking areas of the five airports with designated smoking areas and five times the average level in smoke-free airports. Smoke-free policies at the state, local, or airport authority levels can eliminate involuntary exposure to SHS inside airports and protect employees and travelers of all ages from SHS.