Background: The purpose of this study was to evaluate prenatal to postnatal changes in first-time parents' physical and mental health, and to describe social and health predictors of parents' postpartum health. Methods: This prospective study surveyed 261 expectant fathers and mothers during pregnancy and again at 6 months' postpartum regarding their health, partner, and work characteristics. Postpartum changes in health were evaluated by paired t tests, and predictors of postpartum health were determined using multiple regression analyses. Results: Both fathers and mothers experienced significant postpartum declines in perceived quality of life. In addition, fathers reported an increase in the number of days ill and a decrease in general health and vitality after childbirth. Mothers perceived an increase in vitality despite their diminishing sleep. Parents' postpartum health was associated with mothers' partner satisfaction, fewer illness days, and certain work characteristics, such as total work time and the balance of work between mothers and fathers. Conclusions: Both mothers and fathers experienced declines in health that persisted at least 6 months after the birth of their first child. Notably, postpartum health was associated with partner satisfaction and work characteristics. This information might be used to develop interventions for improving parents' health during this vulnerable time.