Objective: To investigate direct and moderating effects of risk and resistance factors on the adjustment of mothers of children with obstetrical brachial plexus injuries (OBPI). Participants: Fifty-three mothers of children with OBPI recruited from an OBPI clinic in an Australian pediatric hospital. Measures: OBPI Severity Scale, Parents of Children With Disabilities Inventory, Family APGAR, Short Form Social Support Questionnaire-6, Life Orientation Test-Revised, Perceived Control of Internal States Scale, General Health Questionnaire-12. Results: The factors explained 30% of maternal adjustment variation. Resistance factors explained a unique 18%. Optimism was the only significant moderator. Conclusions: Findings confirm the importance of risk and resistance factors in maternal adjustment and enhance understanding by identifying optimism as a moderator of the risk/adjustment relationship. Interventions promoting optimism may facilitate maternal adjustment.