We investigated how mothers' and fathers' depressed mood and father-child and mother-child relationship predicted preschool children's problem behavior. The sample was 11,286 continuously intact, two-parent biological families of the United Kingdom's Millennium Cohort Study. We found that mother-child relationship and maternal depressed mood had larger effects on children's problem behavior than father-child relationship and paternal depressed mood. The effect of paternal depressed mood was completely mediated by quality of father-child relationship. There were significant moderator effects but only on internalizing problems. There was little evidence to suggest that, among children of this developmental stage, quality of father-child relationship buffers the effect of contextual risk (i.e., promotes resilience). Quality of mother-child relationship, in contrast, buffered the effect of socioeconomic disadvantage but only on emotional symptoms. (Contains 6 figures and 1 table.)