The electrocardiographic findings in patients with verified familial amyloidotic polyneuropathy, from a defined population in northern Sweden with an extremely high prevalence of this disease, were studied. The first electrocardiogram registered, after the diagnosis has been established, was reviewed in 105 patients. In 61 patients, there was at least 1 additional electrocardiogram registered more than 3 years after the first, and the latest of these were also reviewed. Mean follow-up time was 8.2 years. The proportion of patients with an abnormal or suspected abnormal electrocardiogram was 54% at the initial examination and 80% at follow-up. The most common findings at onset of symptoms were atrioventricular and intraventricular conduction abnormalities (33%), S-T depression (20%), flattened or inverted T waves (22%) an prolongation of the Q-T interval (17%). The prevalence of conduction and S-T-T abnormalities increased further during the follow-up period. The occurrence of all electrocardiographic abnormalities was age-related, and there were few abnormalities in patients younger than 55 years. The cardiac conduction disturbances were progressive, and 19 patients had an artificial pacemaker implanted during the follow-up period.