Familial amyloidotic polyneuropathy (FAP) in Swedish patients is associated with the same transthyretin mutation (TTRMet30) as in Portuguese, Japanese, Brazilian and Majorcan patients. Yet, the age of onset of FAP is much later in Sweden than in other populations. We have studied 239 cases of FAP from northern Sweden, their geographical distribution, differences in age of onset, and estimated prevalence and incidence rates. Cases and families concentrate mainly in two areas, around the towns of Skellefteå and Piteå. Mean age of onset was found to be later in the Piteå (58.8 +/- 10.8) than in the Skellefteå area (54.4 +/- 13.5). Unusually high figures were found for prevalence rates (91 x 10(-5) and 104 x 10(-5), respectively) in 1985. Mean yearly incidences were 3.1 x 10(-5) and 4.4 x 10(-5), respectively, over the period 1985-1989.