Very low birth weight (VLBW) infants have more health and developmental problems than normal birth weight full-term infants. These problems are more common in males than female VLBW preterm infants. Male VLBW infants also experience less positive mother-infant interactions than females, especially when mothers are emotionally distressed. This is a significant problem because positive mother-infant interactions function as an important protective factor against the negative health and developmental outcomes associated with prematurity. The source of the vulnerability of male VLBW infants to health problems, suboptimal mother-infant interactions, and poor development goes beyond gender socialization differences and includes biological factors. Identification of infant and maternal biological markers/predictors of infant health and developmental outcomes could ultimately lead to interventions for VLBW preterm infants.