Abstract Purpose: The modified DUKE-UNC Functional Social Support Questionnaire (FSSQ) is considered an assessment tool for patients with schizophrenia. However, it has not been validated in this patient population. This issue is addressed here by examining the tool's psychometric properties in a clinical sample of patients with schizophrenia. Methods: Two hundred and forty-one patients from 10 Adult Mental Health Centres (AMHC) meeting the following inclusion criteria were included: 1) International Classification of Diseases-10 (ICD-10) diagnosis of schizophrenia; 2) Global Assessment of Functioning (GAF) scores ≤50; 3) Illness duration of more than 2 years; and 4) Clinical stability. Patients were evaluated at baseline and at one-year follow-up for clinical and psychosocial variables. Results: The factor analysis revealed two factors that explained 54.15% of the variance. Internal consistency was excellent for the total FSSQ (0.87 at baseline and 0.88 at one year follow-up) and ranged between adeq uate and excellent for FSSQ domains. Correlations between FSSQ scores and those of global functioning, psychiatric symptoms, disability and quality of life ranged between small and large. There were significant differences between groups of patients with schizophrenia in FSSQ scores. Patients with higher levels of somatic complaints and patients who were disabled scored significantly lower in some or all FSSQ scores. After one-year follow-up, patients improved in overall functioning and there was a decrease in psychiatric symptoms. Conclusions: The FSSQ is a reliable and valid instrument for the assessment of perceived social support in patients with schizophrenia.