The trend of fertility in Wales and the Southern and Midland counties of England was demonstrated and discussed in the previous sections of this enquiry.1 The corresponding vital statistics for Northern England are given in the present concluding section and, in addition, the results that have been found are briefly reviewed for the country as a whole. For the Northern counties the same methods have been employed as in the two previous sections. Briefly, the actual birth-rate has been measured by the number of births per 1000 married women aged 15–45, while as a rough assessment of how far a changing age distribution of married women has affected its level, a potential birth-rate and fertility ratio have also been calculated. The potential birth-rate gives the number of births per 1000 married women aged 15–45 obtained by applying Tait's fertility ratios 48.75, 41.25, 30 and 15 to the number of married women in the age groups 15–19, 20–24, 25–35 and 35–45 respectively. The fertility ratio is the ratio of the actual to the potential birth-rate.