This study tests the idea that mothers' self-efficacy beliefs mediate the effects on parenting behavior of variables such as depression, perceptions of infant temperamental difficulty, and social-marital supports. Subjects were 48 clinically depressed and 38 nondepressed mothers observed in interaction with their 3-13-month-old infants (M = 7.35 months). As predicted, maternal self-efficacy beliefs related significantly to maternal behavioral competence independent of the effects of other variables. When the effects of self-efficacy were controlled, parenting competence no longer related significantly to social-marital supports or maternal depression. In addition, maternal self-efficacy correlated significantly with perceptions of infant difficulty after controlling for family demographic variables. These results suggest that maternal self-efficacy mediates relations between maternal competence and other psychosocial variables and may play a crucial role in determining parenting behavior and infant psychosocial risk.