Data on pacemaker implantation were obtained from the Medical Device Implant Supplement to the 1988 National Health Interview Survey, a nationally representative, population-based survey of 47,485 households (122,310 persons). The survey yielded an estimate of 456,482 noninstitutionalized adults with pacemakers (prevalence, 2.6 per 1,000). Prevalence rose significantly with age, from 0.4 per 1,000 among persons ages 18-64 to 26 per 1,000 among those ages 75 or older. Age-adjusted prevalence in males was 1.5 times that in females, and in whites 1.6 times that in nonwhites, although these differences were of borderline statistical significance. Prevalence did not vary significantly by region of residence, educational level, or income, but was significantly increased (more than threefold) in those reporting any activity limitation compared with those with no limitation. Fifteen percent of pacemakers in use were replacements; about one-fifth of these had been replaced more than twice. Sixty percent of previous pacemakers had been in place for at least 5 years. These data provide the first nationwide, population-based estimates of the epidemiology of pacemaker implantation, focusing particularly on the demographics of U.S. pacemaker recipients.