The transition to parenthood is considered normal; however, it includes the need for parental adjustment. Sometimes this transition can be disturbing and induce high levels of stress. Our research question was How is bonding between the father and baby influenced by vulnerability to stress? We aimed To identify the establishment of bonding between father and baby and to analyze how their emotional involvement can be influenced by vulnerability to stress. Research Methods: This is a quantitative, descriptive-correlational and explanatory study, with a non-probabilistic convenience sample (N= 349 fathers), with a mean age of 31.84 years (SD= 6.067). Data is collected by a questionnaire applied up to 48 hours after birth, including socio-demographic, parent involvement and obstetric characterization, the Bonding Scale and the Vulnerability to Stress Scale -23 QVS. Younger participants, who became fathers for the first time, were involved in the pregnancy and spoke with the baby during the gestational period demonstrated higher levels of positive bonding. It is not clear that those who monitored labor and picked up the child after birth showed high levels of bonding. Functional inhibition and dependency is the only factor which predicts vulnerability to stress. Bonding is a complex process which may be influenced by context and degree of involvement during pregnancy and childbirth. Vulnerability to paternal stress is multidetermined and may be accentuated in this period of transition to parenthood. Encouragement by health professionals in the father's emotional involvement with the baby and in early detection of vulnerability to stress is pertinent.