Background: Experience in institutional/orphanage care has been linked to increased mental health problems. Research suggests that children adopted from institutions experience specific difficulties related to inattention/overactivity. Evidence of internalizing and conduct problems relative to non-adopted peers has been found in early childhood and early adolescence, but problems may not differ from other adopted children. This study clarifies the understanding of behavioral and emotional symptoms of post-institutionalized (PI) children during middle childhood. Methods: Eight- to eleven-year-old PI children (n = 68) and two comparison groups, children internationally adopted from foster care (n = 74) and non-adopted children (n = 76), and their parents completed the MacArthur Health and Behavior Questionnaire related to attention-deficit/hyperactivity disorder (ADHD), externalizing, and internalizing symptoms. Group means for symptom level and number of children with symptoms above clinical cutoffs were compared. Results: PI children displayed an increased level of ADHD symptoms per parent report. PI child and parent report indicated a higher number of PI children above clinical ADHD cutoff. Both groups of internationally adopted (IA) children had higher levels of externalizing symptoms relative to non-adopted children, with parent report indicating higher numbers of IA children above the externalizing clinical threshold. Informants differed in their report of internalizing symptoms. Parents indicated that both IA groups displayed increased internalizing symptom levels and greater numbers above clinical threshold; however, children reported this to be true only for the PI group. Conclusions: PI children differ from non-adopted peers across symptom domains in middle childhood. Whether these concerns were more broadly associated with international adoption rather than institutional care depended on symptom domain and informant. An understanding of this variability may be beneficial for treatment and intervention. (Contains 2 tables.)