This study examined whether mothers' endorsement of negative cognitive errors and positive illusions uniquely contribute to explaining the impact of parenting daily hassles on parenting adjustment in 72 mothers of children ages 2–5 years. Although scores on both scales of biased appraisals correlated significantly with reported frequency and intensity of parenting daily hassles, only mothers' endorsement of negative cognitive errors consistently and uniquely predicted higher levels of psychological distress and parenting stress and lower levels of parenting satisfaction and self-efficacy more than either frequency or intensity of parenting hassles alone. These results suggest both promises for parenting interventions and further integration of theories of stress, negatively biased appraisals, and psychological adjustment with the parenting literature.