Head irradiation, the acceptable mode of treatment for tinea capitis in the past, is recognized today as a causative factor for meningioma. This treatment was applied en mass to immigrants coming to Israel from North Africa and the Middle East during the 1950s. In order to estimate the effect of the differential radiation treatment on the rates of meningioma in the total population, the authors assessed time trends of this disease in Israel over the past 40 years by main ethnic origin. Cohort analysis shows a marked incidence rise in the North African-born cohorts born in 1940-1954 starting from the 1980s. A similar pattern is seen in the Middle Eastern born, although the increase is not as sharp. In consequence, there is a crossover of the interethnic incidence curves in the 1940-1949 cohort. Comparison of the relative risk between 1940-1954 cohorts that comprised most of the irradiated with 1930-1939 cohorts, who were largely free of the radiation, shows that the North African born have the largest relative risk of 4.62, followed by the Middle Eastern born, with a relative risk of 1.95, while the European-American born have a relative risk close to 1. The differences between the three areas of birth are statistically significant. The data illustrate the potential risk of administering highly potent therapy for an essentially benign disease that led, in turn, to a drastic change in the national meningioma pattern.