There is conflicting evidence regarding the effect of coeliac disease (CD) in the father on birthweight and preterm birth. We investigated the association between paternal CD and birthweight and preterm birth. Medical records of all singleton live-born children in Denmark between 1 January 1979 and 31 December 2004 were linked to information about parents' diseases. Fathers who were diagnosed with CD were then identified. Fathers with CD were considered treated if they were diagnosed before pregnancy and untreated if they were diagnosed after the date of conception. The outcome measures were: birthweight, small-for-gestational age (birthweight