PIP: The systematic recording of birthweight seems to have begun in Paris in 1802 and now birthweight is an essential piece of information which is part of the statutory notification of birth. Low birthweight infants make a disproportionate contribution to perinatal mortality. Reducing the incidence of low birthweight is more significant, clinically, than a rise in mean birthweight. Genetic factors, important in determining ultimate size, do not seem to have much influence on birthweight. The variation in birthweight between different ethnic groups is well documented. Meredith (1970) reviewed the world literature. Low mean birthweights were recorded almost exclusively in Africa, India, and the Far East, whereas the high means occurred mainly among Europeans and white Americans. In areas with high levels of immigration, medical professionals are conscious of the need for accurate information about ethnic groups, but the subject is associated with numerous problems. To compare ethnic groups, for whatever purpose , the epidemiologist needs to negotiate a "minefield" of social variables, nutritional uncertainties, and racial sensitivities. The members of a given ethnic group share both a genetic inheritance and a similar geographical, social, and cultural background. All of these must be considered. Immigration has provided an opportunity to study the effect of social and cultural adaptation and to identify those features which are apparently immutable. At the recent conference at the Royal College of Obstetricians and Gynecologists on the obstetric problems of Asian immigrants in Britain, it was shown that poor fetal growth is associated with deficiencies of minerals and protein due to dietary habits. Viegas et al. (1982) suggested that birthweights can be increased by giving protein supplements to Asian women during the 3rd trimester. In Israel the problems are very different. Israel contains a variety of immigrants at various stages of cultural assimilation. Marked differences have been observed between Jewish immigrants from Europe, the US, North Africa, and the Middle East who, although all Jewish, differed in cultural and genetic background. Babies born to mothers who came from North Africa were, on the average, heavier than those of other ethnic groups, in spite of lower social class. Yet, the birthweight advantage was eroded with adaptation to Israeli culture. The issue is whether these differences in birthweight matter.