The current study examined trajectories of maternal and paternal depression in the year following the birth of an infant sibling, and relations with family risk factors and firstborn children's internalizing and externalizing behavior problems. Latent class growth analysis was conducted on 231 families in a longitudinal investigation (prebirth and 1, 4, 8, and 12 months postbirth) and revealed four classes of families: both mother and father low in depressive symptoms (40.7%); mother high–father low (25.1%); father high–mother low (24.7%), and both mother and father high (9.5%). Families with both mothers and fathers high on depressive symptoms were higher on marital negativity, parenting stress, and children's internalizing and externalizing problems, and lower on marital positivity and parental efficacy than other classes. Children, parents, and marital relationships were more problematic in families with fathers higher on depressive symptoms than in families in which mothers were higher, indicating the significant role of paternal support for firstborn children undergoing the transition to siblinghood. Maternal and paternal depression covaried with an accumulation of family risks over time, no doubt increasing the likelihood of children's problematic adjustment after the birth of their infant sibling.