Objective: In the developmental traumatology model, the biological construct of sex is considered a moderator that may negatively influence child maltreatment sequelae including those pertaining to neurocognitive function. Method: This study examined sex-differences in neurocognitive function and behavior problems in maltreated boys (n = 42), maltreated girls (n = 56) versus nonmaltreated boys (n = 45) and girls (n = 59). Maltreated boys were hypothesized to have poorer neurocognitive functioning than maltreated girls, and nonmaltreated boys and girls, in all neurocognitive domains, particularly pertaining to executive function and attention. We also examined correlations between cognitive function and parent report of child behavior problems for maltreated and nonmaltreated children. Results: Maltreated boys performed more poorly on measures of intelligence, attention, language, memory, executive function, and academic achievement in both reading and math than nonmaltreated boys. Maltreated boys did not perform more poorly on these cognitive measures or behavioral measures than maltreated girls, except for one memory measure. Maltreated girls performed more poorly on measures of intelligence, language, memory, executive function, and academic achievement than nonmaltreated girls. Maltreated girls with better visual-spatial skills had more internalizing and externalizing problems. Effect sizes for these sex differences ranged from small to large. Conclusions: Both maltreated boys and girls showed poorer cognitive function than their nonmaltreated sex-matched controls. Maltreated girls had subtle sparing of attention and short-term memory (STM). Understanding sex differences in neurocognitive functioning may have implications for designing large population studies of maltreated youth.