Behavioral problems in young children can take on a variety of forms, which are linked to distinct antecedents and co-occurring markers. Internalizing difficulties in young children, for example, have been linked to individual differences in infant temperament and cortisol levels. In addition, there is growing evidence that these biobehavioral mechanisms are also shaped by gender. Four-year-old children participated in a study examining the relations between salivary cortisol and behavioral maladjustment as a function of gender and temperament. Both longitudinal (maternal report of infant temperament at 9 months) and concurrent (morning salivary cortisol at age 4) data were used to predict two forms of maladjustment: 'Withdrawal' (maternal report of internalizing behavior and laboratory observation of social reticence) and 'Acting Out' (maternal report of externalizing behavior and laboratory observation of solitary active play). High basal cortisol levels were strongly associated with Withdrawal in male participants. However, the relation was significant only in boys who exhibited high levels of negative temperament in infancy. There were no comparable findings with 'Acting Out' beyond a main effect of gender reflecting greater difficulty in boys. The data suggested that there are unique biobehavioral mechanisms shaping specific patterns of maladjustment in childhood.