A 25 item version of the maternal behavior Q-set (MBQS) was validated with 40 adolescent mother-infant dyads. Observations were made from 10 min play interactions when infants were 10 months old. Results show that the short MBQS is reliable (r(i)=.94), is related to assessments using the full MBQS at 6 months (r=.35), to cognitive development at 10 and 15 months (r=.48), and attachment security at 15 months (r=.34), indicating appropriate psychometric characteristics.