Epidemiological studies of Multiple Sclerosis (MS) in the United States have shown an association with urban living and higher socio-economic groups and a higher incidence and earlier age at onset of symptoms in women. This study is based on the proposition that these trends may be a consequence of differences in exposure to an etiological factor around 15 years of age. As a result of variations in related United States and New Zealand data and other pertinent observations the possibility of a link between high childhood milk intake followed by a large or sudden reduction during the adolescent growth spurt, and the subsequent incidence of MS in young adults is proposed. The possible involvement of calcium and lead metabolism is also discussed. It may be that the elusive environmental variable associated with the incidence of MS is partly a behavioural one related to western social attitudes.