M,fORTALITY rates from diseases of advanced life in the United States are uniformly higher among the foreign born than among the native born. Furthermore, the mortality rates from these causes are much higher among the Irish and German born than among those born in Italy, Poland and the former Austro-Hungarian empire. In view of these surface indications investigators have frequently assumed that the foreign nationals in the United States,-and particularly the Irish and Germans, were particularly subject to whatever disease happened to be in question. In making these statements such investigators have lost sight of the rather obvious fact that the foreign born are on the average older than the native born. The native born population is regularly distributed with regard to age with the largest number in the first age group and numbers diminishing steadily with advancing years. The foreign born population on the other hand is small in the age group under 5 years, since the children of the foreign born are themselves usually native born. In the population of Pennsylvania in 1920 the median age of the native born whites was 21.4 years, with quartiles at 9.3 and 39.0, while in the foreign born population the median age was 38.4 years, with quartiles at 29.4 and 49.8. In 1927 there were, according to the state tabulation, 9,283 deaths in Pennsylvania from cancer and 20,771 from heart disease, giving crude death rates.for these causes of 95.4 and 214.0 per 100,000 population. The median age at death from cancer was 62.2 years and from heart disease 66.3 years. The crude death rates by nativity for cancer were, native born 81.2 and foreign born 180.2, and for heart disease, native born 184.0 and foreign born 382.3 per 100,000 population. But by computing age specific death rates, multiplying these rates by the estimated native and foreign population at each age group and adding the products, it is found that on the basis of age alone the expected number of cancer deaths by nativity would be 7,096 native born and 2,187 foreign born. The actual figures were 6,843 native born, 2,343 foreign born and 97 unspecified. For heart disease the expected distribution of deaths was native 16,024 and