The co-occurrence of behaviors of attention-deficit/hyperactivity disorder (ADHD) with behaviors of anxiety or behaviors of depression is the norm, but little is known on how the co-occurrence accounted for youths’ peer relations. The authors report results on difficult peer relations in relation to behaviors of ADHD, co-occurring behaviors of depression, and behaviors of anxiety from three studies on 862 youths in China and in the United States. Study 1 included 313 ethnically and socioeconomically diverse American youths; Study 2 included 250 youths who were adopted out of Chinese orphanages by American parents; and Study 3 included 299 youths from Beijing, China. Data on difficult peer relations and behaviors of ADHD, depression, and anxiety were collected with the third edition of Behavior Assessment System for Children-Self Report of Personality. In all three studies, each type of problems alone significantly predicted difficult peer relations, but behaviors of ADHD were not significant when co-occurring behaviors of depression or co-occurring behaviors of anxiety were considered. Despite that the youths in our study had different cultural and personal backgrounds, there was no evidence that behaviors of ADHD were detrimental to youths’ peer relations when behaviors of depression or anxiety were considered. Implications for intervention were discussed.