We compared recent parents (married, cohabiting, not cohabiting but romantically involved, and not romantically involved) to examine the association between mental health problems and relationship status. We analyzed data from the Fragile Families and Child Wellbeing Study that followed a cohort of approximately 4900 births in large US cities. Our study included a large oversample of nonmarital births (n = 3700) and interviews with both mothers and fathers. We used the Composite International Diagnostic Interview Short Form to assess depression and generalized anxiety 1 year after the birth. Self reports were used to measure heavy drinking, illicit drug use, incarceration, and partner violence. Unmarried parents reported more mental health and behavioral problems than did married parents, and unmarried parents whose relationships ended before the birth reported more impairment compared with other groups of unmarried parents. A substantial number of children are born to unmarried parents and are at risk for poor parenting and poor developmental outcomes. Government initiatives aimed at increasing marriage rates among low-income couples need to consider the mental health status of unmarried parents.