This study examined relations between trust beliefs in significant others (TBSO), interpersonal stress, and internalizing psychopathology for adolescents with psychiatric disorders. Two hundred and thirty-four adolescents from an acute inpatient unit (154 females, Mage = 14.72 years, SD = 1.39 years) completed standardized scales/interviews that assessed TBSO (mother, father, teacher, peers and TBSO as a total score), interpersonal stress, and internalizing psychopathology. It was found that adolescents’ TBSO and trust beliefs in each significant other were negatively associated with interpersonal stress and internalizing psychopathology. The findings confirmed that the relation between the adolescents’ interpersonal stress and internalizing psychopathology was moderated by TBSO, trust beliefs in mother, and trust beliefs in peers. The findings supported the conclusion that holding elevated TBSO (particularly trust beliefs in mother and peers) by adolescents with psychiatric disorders promotes their psychosocial adjustment including their resilience to the effects of interpersonal stress on internalizing psychopathology.