The incidence and mortality of multiple sclerosis in south east Wales.

The incidence of multiple sclerosis was shown to be 8.2/10(5)/year (definite or probable 5.4 and suspected 2.8/10(5)/year) during a 3 year prospective study carried out in an area of south east Wales which has a high prevalence of the disease (120/10(5). Mortality in affected individuals who were prevalent at the start of the survey was 3.1/10(5)/year; many deaths resulted from direct complications of multiple sclerosis but 38% were due to unrelated causes. The rate at which new cases were identified approximately matched deletions from the register arising from death, outward migration and other causes so that prevalence did not change significantly during the survey (1985-1988).