Refugees often experience high levels of trauma and overall stress that contribute to disproportionate risk for mental health problems. Despite a 136% increase in the number of Somali refugees over the past quarter century, culturally appropriate mental health screening and assessment instruments for use with this population remain limited. This study applies multidimensional item response theory to compare structural models and validity of the Posttraumatic Stress Disorder (PTSD) Checklist—Civilian Version. Data are from a purposive sample of 250 Somali youth living in Nairobi’s Eastleigh Estate in Kenya. Using ConQuest software, we used a multidimensional extension of the Rasch model to test 7 competing models of PTSD in this sample. The four-factor emotional numbing model of PTSD provided the best fit for the data; there was no differential item functioning by sex or birth country. We found support for convergent validity, and canonical correlations generally supported theoretically expected relationships between PTSD Checklist—Civilian Version subscales and mental health and trauma-related measures. Identification of numbing, as a dimension distinct from effortful avoidance, permits a more refined determination of PTSD in this population. This finding can guide the development and implementation of targeted interventions. We also discuss the implications for advancing sound measurement of PTSD among Somali refugee youth. (PsycINFO Database Record (c) 2019 APA, all rights reserved)