Background: Healthcare professionals in neonatal intensive care units (NICUs) tend to focus attention on the mothers and the newborn infants. Thus, fathers may find it difficult to establish an optimal father–child relationship and their stress may increase and persist during hospitalization. Purpose: To investigate the impact of a more father-friendly NICU on paternal stress and their participation in childcare. Methods: A quasiexperimental design was conducted on Danish-speaking fathers of newborn infants 28 or more weeks' gestational age. The Parental Stressor Scale: Neonatal Intensive Care Unit (PSS:NICU) was used to measure paternal perceptions of stressors. Paternal participation in childcare was measured using 7 additional items. The questionnaires were distributed on admission to the NICU, at the 14th day of hospitalization, and at the time of discharge. The primary outcome was the difference in the PSS:NICU overall stress score on admission to the NICU and at the time of discharge in the control group compared with the intervention group. Results: A total of 109 fathers were included. The overall PSS:NICU stress score increased after the intervention. Paternal involvement, staff expectations, and the social expectation to fulfill the traditional role of a breadwinner and additionally of a caregiver may have caused increased stress. Implications for Practice: Healthcare professionals must be aware of the father's need to be an equal coparent. Nurses, as key persons, should motivate and expect fathers to be involved, and support them to establish a father–child relationship, although they might become more stressed. Implications for Research: More adequate outcome measures are needed to determine the effect of interventions on paternal stress.