Occurrence of multiple sclerosis in the north and south of New Zealand.

An impression that multiple sclerosis is commoner in southern parts of New Zealand than in the north has never been tested rigorously. Identical methods were used to determine the prevalence and incidence of multiple sclerosis in two regions: the Waikato (in the North Island) and Otago and Southland (in the South Island). No cases were found in Maoris, while the expected number was 11.7. The prevalence rate of multiple sclerosis (excluding possible cases) in non-Maoris was 24 per 100,000 in the northern region and 69 per 100,000 in the south. The incidence rate was also more than twice as high in the southern region. These findings are considered in relation to genetic and environmental hypotheses about the aetiology of multiple sclerosis.