Background: Substance use disorders have been described as a chronic and relapsing illness, requiring informal caregiving roles especially in times of acute relapse and treatment. Caregivers of patients with substance use disorders experience financial, physical and psychological stress and strain. Substance use disorders also co-exist with other mental disorders, whose prevalence amongst family members is higher than the general population. There is a dearth of local data on the amount of burden experienced by family caregivers and the prevalence of psychiatric morbidity among family members of persons with substance use disorders in this environment. Aim: The objectives of this study were to ascertain caregiver socio-demographic variables, the level of caregiver burden, the prevalence of probable psychiatric morbidity and the relationship between caregiver burden and probable psychiatric morbidity among family caregivers of patients with substance use disorders attending the outpatient drug addiction treatment facility at the Neuropsychiatric Hospital, Aro, Abeokuta, Nigeria. Methods: A total population study of one hundred and sixty-nine consenting family caregivers of patients with a diagnosis of substance use disorders, with or without a co-occurring disorder were recruited through the outpatient clinics and DATER Drug Clinics at the Neuropsychiatric Hospital, Aro, Abeokuta. Socio-demographic and clinical variables were recorded for each participant. Family Burden Interview Schedule (FBIS) was used to assess caregiver burden and General Health Questionnaire (GHQ) -28 was used to assess probable psychiatric morbidity. Results: The results showed a mean age of caregivers of 46.9 years, a larger proportion of whom were male, with a partner, of Yoruba ethnic extraction, adherents of the Christian faith, with tertiary and postgraduate education, skilled or highly skilled professionals and were i related to the patients as either parent / spouse. The mean duration of illness in patients was 6.69 years, average number of hours per week spent with patients at home was 78.78 hours, and patient had been receiving treatment at the site of study for a mean duration of 12 months. Mean burden score was 20.46, while financial burden score was 6.31, disruption in family activities was 4.59, disruption of family leisure was 3.46, disruption of family interaction was 4.05, effect on physical health of others was 0.92 and effect on mental health of others was 0.95. This study reported a probable psychiatric morbidity of 26.6%, and no significant correlation was found between caregiver burden and probable psychiatric morbidity. Conclusion: The study suggests a need for sensitization of substance use treatment providers to evaluate and treat caregivers of dependent patients who come in contact with treatment facilities. Key words: Substance Use Disorder, Caregiver Burden, Psychiatric Morbidity.