Abstract
The fraction of malformed births (deaths due to congenital malformation divided by births) is shown to vary over the earth with background radiation. Cosmic-ray energy flux is taken as the measure of background. The relation between the world-wide incidence of congenital malformation and geomagnetic latitude yields a X2 = 21 (P < 0·0001) and is in agreement with the approximate theoretical relation. Lines of equal incidence of congenital malformation show characteristics which match variations in the earth's magnetic field or background radiation. Since the variation from 0·3 malformed births per 1000 in South-east Asia to 7·9 in Northern Ireland can be attributed to background, at least 96 per cent of all deaths due to congenital malformation can be attributed to background. The distribution of congenital malformation within the United States provides corroborative evidence. X-rays have caused a 6 per cent increase in congenital malformation in the United States in the last 30 years.