Abstract
A population-based survey of multiple sclerosis in the county of South Glamorgan has demonstrated a prevalence of 441/376718 (117/10(5)). Eighty six per cent of the patients (101/10(5)) had definite or probable disease and 14% (16/10(5)) had suspected multiple sclerosis on 1 January 1985. The estimated average incidence is 5.41/10(5)/year for the period 1947-84 and it has risen significantly over four decades. The prevalence is similar to that found in a recent survey from the south east of England but significantly lower than revised figures from Scotland.