This case-control study was aimed at identifying environmental risk fa
ctors for multiple sclerosis (MS). Ninety-three Israeli-born MS patien
ts identified in country-wide studies and 94 age- and sex-matched cont
rols were interviewed. The questionnaire covered a large span of facto
rs at ages 0, 10 and onset of the disease, with particular emphasis on
socioeconomic status (SES) and sanitary conditions (SAN). A significa
ntly larger percentage of patients reported frequent respiratory disea
ses. Patients and their parents had significantly (p < 0.01) higher ed
ucational levels than controls. The SES and SAN at age 10 were also sy
stematically higher among patients, but significance was reached only
when the frequencies of conditions indicating extremely low values of
SES or SAN were compared. It is possible that the protective effect of
low SES and SAN on risk of MS can be detected only when living condit
ions are well below average, as is frequent in developing countries.