BACKGROUND AND OBJECTIVES: Extremely preterm infants and infants born to adolescent mothers are at risk for adverse developmental. The objectives were to evaluate development and behavior outcomes of extremely low birth weight (ELBW) infants born to adolescent mothers <20 compared with adult mothers ≥20 years and to identify socioeconomic risk factors that affect outcomes. METHODS: Retrospective cohort analysis of 211 infants >27 weeks of adolescent mothers and 1723 infants of adult mothers at Neonatal Research Network centers from 2008 to 2011. Groups were compared and regression models were run to predict 18- to 22-month adverse outcomes. Primary outcomes were Bayley-III scores, neurodevelopmental impairment, and Brief Infant Toddler Social Emotional Assessment problem scores (BITSEA/P) ≥75th percentile. RESULTS: Adolescent mothers were more often single, Hispanic, less educated, and had public insurance. By 18 to 22 months, their children had significantly increased rates of having lived ≥3 places (21% vs 9%), state supervision (7% vs 3%), rehospitalization (56% vs 46%), and BITSEA/P ≥75th percentile (50% vs 32%) and nonsignificant Bayley-III language scores <85 (56% vs 49%, P = .07). In regression analysis, children of adolescent mothers were more likely to have BITSEA/P ≥75th percentile (relative risk 1.50, 95% confidence interval 1.08-2.07). Living ≥3 places and nonwhite race were predictors of adverse behavior. State supervision was an independent predictor of each Bayley-III composite <70 and neurodevelopmental impairment. CONCLUSIONS: ELBW infants of adolescent mothers experience high social and environmental risks that are associated with adverse behavior outcomes. These findings inform the need for comprehensive follow-up, coordinated care services, and behavior interventions for ELBW infants of adolescent mothers.