BACKGROUND: The majority of research on HIV/AIDS and mental health has been carried out among clinical populations: the time of onset of comorbid depression and the mechanisms for this are therefore unclear. Although there is evidence to suggest that asymptomatic people living with HIV/AIDS exhibit some cognitive deficits, the prevalence of poor cognitive functioning among people in low income settings at an early, pre-clinical stage has not yet been investigated. METHODS: We used a cross-sectional survey design to test the hypotheses that symptoms of Common Mental Disorder (CMD) and low scores on cognitive tests would be associated with seropositivity among participants coming for testing for HIV/AIDS. Participants were recruited at the time of coming for testing for HIV/AIDS; voluntary informed consent was sought for participation in research interviews and data linkage with HIV test results. Baseline questionnaires including sociodemographic variables and measures of mental health (PHQ-9, GAD-7, panic disorder questions, AUDIT and delayed word list learning and recall and animal naming test of verbal fluency) were administered by trained interviews. HIV status data was extracted from clinical records. RESULTS: CMD and scoring below the educational norm on the test of verbal fluency were associated with testing positive for HIV/AIDS in bivariate analysis (OR = 2.26, 1.31-3.93; OR = 1.77, 1.26-2.48, respectively). After controlling for the effects of confounders, the association between CMD and seropositivity was no longer statistically significant (AOR = 1.56, 0.86-2.85). After adjusting for the effects of confounders, the association between low scores on the test of verbal fluency and seropositivity was retained (AOR = 1.77, 1.27-2.48). CONCLUSIONS: Our findings provide tentative evidence to suggest that low cognitive test scores (and possibly depressive symptoms) may be associated with HIV status among people who have yet to receive their HIV test results. Impaired cognitive functioning and depression-like symptoms may be the result of the same underlying neurological damage. CMD and cognitive impairment may overlap to a greater extent than previously assumed. If replicated, this may have implications for the way in which we measure and treat CMD and cognitive functioning among people living with HIV/AIDS.