In 2003 and 2004 two measles outbreaks occurred in Jewish ultra-orthodox communities in Jerusalem. The index case of the first outbreak (March 2003) was a 2-year-old unvaccinated child from Switzerland. Within 5 months, 107 cases (mean age 8·3±7·5 years) emerged in three crowded neighbourhoods. The first cases of the second outbreak (June 2004) were in three girls aged 4–5 years in one kindergarten in another community. By November 2004, 117 cases (mean age 7·3±6·5 years) occurred. The virus genotypes were D8 and D4 respectively. Altogether, 96 households accounted for the two outbreaks, with two or more patients per family in 79% of cases. Most cases (91·5%) were unvaccinated. Immunization coverage was lower in outbreak than in non-outbreak neighbourhoods (88·3% vs. 90·3%, P=0·001). Controlling the outbreaks necessitated a culture-sensitive approach, and targeted efforts increased MMR vaccine coverage (first dose) to 95·2%. Despite high national immunization coverage (94–95%), special attention to specific sub-populations is essential.