There is a high prevalence of substance abuse and psychiatric disorders among HIV-infected individuals. Importantly, drug and alcohol-use disorders are frequently co-morbid with depression, anxiety and severe mental illness. Not only do these disorders increase the risk of contracting HIV, they have also been associated with decreased highly active antiretroviral therapy (HAART) utilisation, adherence and virological suppression. The literature evaluating the relationship between substance abuse and HIV outcomes has primarily focused on injection drug users, although there has been increasing interest in alcohol, cocaine and marijuana. Similarly, the mental health literature has focused largely on depression, with a lesser focus on severe mental illness or anxiety. To date, there is little literature evaluating the association between co-occurring HIV, substance abuse and mental illness on HAART uptake, adherence and virological suppression. Adherence interventions in these populations have demonstrated mixed efficacy. Both directly observed therapy and pharmacist-assisted interventions appear promising, as do integrated behavioural interventions. However, the current intervention literature has several limitations: few of these studies are randomised, controlled trials; the sample sizes have generally been small; and co-occurring substance abuse and mental illness has not specifically been targeted in these studies. Future studies examining individual substances of abuse, psychiatric disorders and co-occurring substance abuse and psychiatric disorders on HIV outcomes will inform targeted adherence interventions.