Polyvictimization involves experiencing multiple forms of maltreatment or other interpersonal victimization, and places children at risk for severe psychosocial impairment. Children with psychiatric problems are at risk for polyvictimization, and polyvictimized child psychiatric inpatients have been found to have particularly severe psychiatric symptoms. Cluster analysis was used to identify a polyvictimized subgroup (N = 22, 8%) among 295 outpatient admissions in 2007–2009 to a child psychiatry outpatient clinic, based on chart review of documented maltreatment, parental impairment (history of arrest, psychiatric illness, and substance use), and multiple out-of-home placements. Polyvictimization was associated with severe parent-reported externalizing problems and clinician-rated psychosocial impairment, independent of demographics and psychiatric diagnoses. Posttraumatic stress disorder (PTSD) was the only psychiatric diagnosis associated with polyvictimization. Polyvictimization merits further clinical and research assessment with child psychiatry outpatients. Evidence-based PTSD assessment and treatment for polyvictimized children with adaptations to address their severe impairment and externalizing problems also warrants empirical evaluation.