Further evidence in support of the hypothesis that one cause of multiple sclerosis is childhood infection.

Consideration is given to: (1) the multiple sclerosis (MS) incidence rate in dizygotic (DZ) twins, (2) the DZ twin concordance rate in MS, (3) MS and birth order and (4) MS rates on islands. All four sorts of data are consistent with (indeed would be predicted by) the hypothesis that MS is a sequel of late (rather than early) exposure to childhood infection.