Due to the increased effectiveness of and access to antiretroviral therapy (ART), people with HIV (PWH) are living longer. As a result, the population of older PWH has increased. Mental and substance use disorders (MSDs) are common and frequently co-occurring among PWH and are associated with poor HIV care outcomes. Research into the prevalence and co-occurrence of MSDs among ageing PWH remains limited, particularly in low- and middle-income countries (LMICs). We analysed data collected between 2020 and 2022 from the International epidemiology Databases to Evaluate AIDS (IeDEA) Sentinel Research Network cohort of PWH aged 40 years or older on ART at 11 HIV clinics in Brazil, Côte d'Ivoire, India, Kenya, Mexico, Uganda, Rwanda, Togo, Vietnam, Zambia and Zimbabwe. We estimated the prevalence and co-occurrence of unhealthy alcohol use (AUDIT-C ≥3 for women, ≥4 for men), unhealthy drug use (ASSIST >3 for cannabis, cocaine, amphetamines, inhalants, sedatives, hallucinogens and/or opioids), and moderate to severe symptoms of depression (PHQ-9 ≥10), anxiety (GAD-7 ≥10) and post-traumatic stress disorder (PTSD) (PCL-5 ≥33). Psychiatric multimorbidity was defined as having symptoms of two or more disorders assessed. Log binomial models assessed the association between socio-demographic and HIV care characteristics and symptoms of anxiety, depression, PTSD or unhealthy substance use. Of 2821 participants, the prevalence of unhealthy alcohol and drug use was 21% and 5%, respectively. The prevalence of moderate to severe symptoms of depression, anxiety and PTSD was 14%, 9% and 6%, respectively. Overall, the prevalence of psychiatric multimorbidity was 11%. Among those with symptoms of at least one mental health or substance use outcome assessed (n = 1036), the prevalence of psychiatric multimorbidity was 31%. In binomial models, the prevalence of symptoms of depression and anxiety was higher, while the prevalence of unhealthy alcohol and drug use was lower among women than men. Unhealthy alcohol use and symptoms of depression were most commonly reported, among this cohort of PWH aged 40 or older across 11 LMICs. Integration of MSD screening and treatment into HIV care should be prioritized. The effectiveness and implementation of transdiagnostic or multi-focus mental health treatment approaches in HIV care settings should be examined.< Réduire