Time to pregnancy according to the age of the father and the mother has been studied among 10,886 couples from Odense and Aalborg. Late in their pregnancy (36th week) all woman in the two cities were given a questionnaire on time to pregnancy as well as a number of other items. Eighty-six percent responded to this questionnaire, and data concerning previous pregnancies, the outcome of the pregnancy in question, etc., were later collected from medical files. The study showed a strong correlation between mother's age and subfecundity, even after adjustment for a number of potential confounders. The association between subfecundity and the age of the father was much weaker and did not reach statistical significance. Interpretations and implications of these findings are discussed in the paper.