Introduction: Adolescent secondhand smoke exposure (SHSe) is associated with smoking initiation and independently damages health. Methods: We used data from the school-based 2003-2004 Israel National Health and Nutrition Youth survey (MABAT) to examine patterns and determinants of SHSe in a multiethnic sample of Israeli adolescents. School and child response rates were high (school: 91.8%, child: 87.9%), with 6,274 participants. We used generalized estimating equations to examine SHSe determinants. Results: Most Israeli adolescents were exposed to SHS (total: 85.6%; home: 40%; school: 31.4%; entertainment: 73.3%; other: 16.3%). Exposure patterns differed between the Jewish and non-Jewish sectors. Jews were more frequently exposed at school and entertainment venues than were non-Jews but were less frequently exposed at home. Druze were the least exposed and non-Arab Christians the most exposed. Secular Jews were more exposed than were religious Jews; the opposite was true among Arabs. Children of less-educated fathers were exposed more than children of more-educated fathers. Adolescents who smoked were more exposed than were nonsmokers. Conclusions: The high levels of SHSe among Israeli adolescents were characterized by different patterns of exposure among different population groups. Interventions to reduce adolescent SHSe, with appropriate tailoring, are urgently needed. These findings provide support for sustainable implementation of the recent governmentally approved tobacco control plan, which includes extended legislation for, and increased enforcement of, laws about smoking bans in schools and entertainment venues. Researchers elsewhere should be aware that levels and patterns of SHSe may vary greatly by subpopulation.