We employed a retrospective cohort design to estimate the prevalence and economic burden of bronchiectasis. Data were obtained from the health-care claims processing systems of more than 30 US health plans (with a combined total of 5.6 million covered lives) and spanned the period January 1, 1999, to December 31, 2001. Study subjects consisted of all persons who were aged ≥18 years in 2001 and had diagnoses of bronchiectasis between 1999 and 2001; those with diagnoses of cystic fibrosis were excluded. For purposes of comparison, a cohort of persons without diagnoses of bronchiectasis was randomly selected and matched on age, sex, geographic region, and comorbid conditions. Prevalence of bronchiectasis ranged from 4.2 per 100,000 persons aged 18–34 years to 271.8 per 100,000 among those aged ≥75 years. Prevalence was higher among women than men at all ages. Persons with bronchiectasis averaged 2.0 (95% confidence interval 1.7–2.3) additional days in hospital, 6.1 (6.0–6.1) additional outpatient encounters, and 27.2 (25.0–29.1) more days of antibiotic therapy than those without the disorder in 2001; average total medical-care expenditures were $5681 ($4862–$6593) higher for bronchiectasis patients. Our findings suggest that over 110,000 persons in the United States may be receiving treatment for bronchiectasis, resulting in additional medical-care expenditures of $630 million annually.