We describe the demography, health, pregnancy behaviours, family histories, and intentions for their children, of the 4401 partners who were enrolled antenatally into Growing Up in New Zealand, New Zealand’s new birth cohort study. The prospective fathers and their pregnant partners had similar demographics. Amongst the prospective fathers there were high rates of obesity, although the majority described themselves as healthy. Higher rates of antenatal depression were present than reported in overseas studies of men. Nearly one-third of the prospective fathers changed their dietary and smoking behaviours during their partners' pregnancies, highlighting an exciting window of opportunity presented by pregnancy to influence health-related lifestyle changes in men. Most expected high level of involvement in the care of their babies, in marked contrast to previous generations of fathers. This baseline description provides a context for understanding the contribution these men, as fathers, will make to the health and wellbeing of their children.