Does preconceptional exposure to ionising radiation before conception affect the health of offspring? Some studies have suggested that radiation exposure might influence the sex ratio at birth, potentially indicating genetic damage. We examined the sex ratio of over 46000 children born to UK nuclear industry workers, using information on exposure from the workers' individual employment and dosimetry records. We found no statistically significant alterations of the sex ratio, and no evidence that exposure to low-level ionising radiation at work influences the sex ratio of children conceived after exposure.