Abstract
The doses per X-ray film given by UNSCEAR (1972) for diagnostic X-ray exposures in pregnancy in Britain have never been justified. Dose per film is an inadequate substitute for a knowledge of dose per examination. Extensive measurements were made in the UK during routine obstetric radiography in 1958 giving a mean fetal whole-body dose of 0.61 cGy in that year. It will have changed little in the next few years. A risk coefficients for childhood cancer caused by X-raying in late pregnancy can then be derived from data for children born in 1958-61. It is 4-5*10-4 per cGy with 95% confidence limits 0.8-9.5*10-4 per cGy and applies equally to cancer incidence and mortality.