Infants of adolescent mothers are at increased risk for negative developmental outcomes. Given the high rate of pregnancy among Mexican-origin adolescent females in the US, the present study examined health characteristics at birth and developmental functioning at 10 months of age in a sample of 205 infants of Mexican-origin adolescent mothers. Infants were relatively healthy at birth and had near average developmental functioning at 10 months. The educational attainment of adolescents and their mothers, and infants' temperamental regulation, promoted positive developmental functioning, while the combination of low adolescent parental self-efficacy and high infant temperamental negativity was associated with greater developmental delay. Findings are discussed with respect to implications for prevention with this at-risk population of mothers and infants. (Contains 3 tables and 1 figure.)