Background: The present study examined the psychometric properties of the Dynamic Risk Outcome Scales (DROS ), an instrument developed to measure dynamic risk factors in individuals with mild intellectual disabilities or borderline intellectual functioning (MID -BIF ) and externalizing (including offending-like) behaviour problems. Method: The sample consisted of 606 clients (86% male) from inpatient treatment wards at a facility for individuals with MID-BIF and externalizing behaviour problems. Results: The DROS showed an acceptable factor structure, good internal consistency, significant test-retest reliability and fair to excellent inter-rater reliabilities for most subscales and total score. Compared to the Adult Behavior Checklist (ABCL; Achenbach & Rescorla, 2003 "Manual for the ASEBA adult forms and profiles." Burlington, VT: University of Vermont, Research Center for Children, Youth, & Families), the DROS showed convergent and divergent validity, concurrent and longitudinal validity. Conclusions: The DROS is a reliable and valid instrument to measure dynamic risk factors in clients with MID-BIF. Future research on the DROS will focus on the assessment of recidivism and the inclusion of internalizing problems.