Research suggests that the attitude of men towards pregnancy, childbirth and child-caring is different from that of women. Up to now, research has focused mainly on motherhood. The aim of this study was to explore first-time fathers’ experiences during early infancy of their children. Grounded theory and constant comparative method were used and 20 fathers aged 20–48 participated. Interviews were carried out in 2002–2003. ‘Changing life’ emerged as the core category consisting of the categories: becoming a father, alternating between work and home, changing relationship towards partner and developing relationship with their child. Changing life implied that they have left bachelor life and become responsible for a child. Becoming a father was much more fantastic than they could have imagined and they suggested that they performed childcare to the same extent as the mother when both parents were at home. Still fathers viewed the mother as the main parent, partly because of their alternating between work and home and because the mothers breast-feed the infants. Fathers’ attitude towards breast-feeding seemed to be ambiguous; it was a matter of necessity, but made them feel insignificant. Changing relationship towards partner was common but it was not necessarily for the worst and often resulted in a more closely united relationship. However, tiredness because of lack of sleep could result in increased irritability towards problems. Developing relationship with their child implied increasing possibilities to learn to know the infant’s signals. Fathers are one of two parents, and hence are important for their child’s growth and development, emotional health and cognitive development. Knowledge about first-time fathers’ experiences during the early infancy of their children may bring about increased support from midwives and child health nurses.