Objective: Confirm the factor structure of the original 18-item Medical Outcome Study Social Support Survey (MOS-SSS) as well as two abbreviated versions in a sample of mothers with a child in mental health treatment. Method: The factor structure, internal consistency, and concurrent validity of the MOS-SSS were assessed using a convenience sample of 330 mothers. Results: A 12-item version that included subscales and a 4-item version maintained a good fit. Conclusion: 12- and 4-item versions of the MOS-SSS are psychometrically sound social support instruments and are appropriate for clinical and research uses. Given the diverse populations that social work serves, confirming instruments in various samples is important to legitimize an instrument's use and advance the evidence base for support interventions. (Contains 7 tables and 1 figure.)