To date, South African research has not examined mental health service provision in substance abuse treatment facilities, even though these services improve client retention and treatment outcomes. To describe the extent to which substance abuse treatment facilities in Gauteng and KwaZulu-Natal provinces provide clients with mental health services during the course of treatment and to compare mental health service provision in these settings by type of facility and staff composition. Cross-sectional audits of substance abuse treatment facilities were conducted in Gauteng and KwaZulu-Natal provinces. Data were collected using the Treatment Services Audit Questionnaire. A response rate of 84% was obtained. Few treatment facilities provide clients with access to mental health services. Inpatient facilities are more likely than outpatient facilities to provide clients with access to mental health services. Facilities with for-profit ownership status are more likely than facilities with non-profit status to provide access to mental health care. Based on the above findings, a number of recommendations are made to increase the provision of mental health services during the course of substance abuse treatment.