Very preterm birth (<32 weeks of gestation) heightens the risk for developmental and behavioral problems, but individual outcomes vary greatly. We evaluated whether mother-toddler dyadic interaction quality, assessed longitudinally at 14, 20, and 30 months (corrected), could account for unique variance in very preterm and full-term children's mental, motor, and behavioral outcomes on the Bayley Scales of Infant Development at 30 months. Participants included 70 mother-toddler dyads (44 with male children, 38 full term and 32 very preterm) followed prospectively from birth to 30 months. In hierarchical regressions controlling for socioeconomic status, dyadic interaction quality at 20 and 30 months explained unique variance in toddlers' 30-month mental scores and was the sole predictor of orientation/engagement and emotion regulation scores. In contrast, very preterm status was the primary predictor of 30-month motor and movement quality scores. Dyadic interaction quality also mediated the association between very preterm status and specific 30-month outcomes. Implications for interventions are discussed.