This study is based on the Reykjavik Study, a long-term prospective cardiovascular survey, which included a representative population of 9135 men and 9627 women, 33-79 years old, who were invited to participate during the years 1967-91. Right bundle branch block (RBBB) was found in 126 men and 67 women. The prevalence increased with age, from 0% among men and women 30-39 years of age to 4.1% and 1.6% in men and women, respectively, who where 75-79 years old. The incidence increased with age. In men younger than 60 years RBBB had a significant relationship with hypertension (P