An outbreak of pertussis encompassing 78 cases in a population of 964 persons living on kibbutz is described. The attack rate was 36.1% among children aged 4 to 11 years, although all had been fully vaccinated. Female predominance and seasonal incidence conformed with what has been reported in the literature. The age distribution, however, was markedly different from that usually observed, indicating that local factors may influence the epidemiology of whooping cough. Despite the seeming paradox of the disease breaking out in a population with a high immunization rate, our results suggest that the vaccine had a protective effect in all age-groups. The incidence of pertussis in Israel in 1987 was considerably higher than that in the United States for the same year, and raises the question of changing the recommendations for vaccination here.