The HIV-1 infections, particularly in the late phase, can be complicated with a range of neurocognitive disorders and behavioural symptoms that become more frequent and severe as the immune system declines and symptomatic illness and AIDS ensue. Nigeria is currently home to about 2.6million HIV infected persons, representing 11% of those living with the virus worldwide, implicating a great burden of persons with HIV-associated neurocognitive disorders. The effects of HAART on cognitive performances among HIV/AIDS patients have not been studied in Nigeria. Studies have shown that some HAART combinations [neuro-HAART] are more beneficial than others in management of HIV-associated neurocognitive disorders. As ARV becomes available the effects of the available combination therapy (HAART) on cognitive function need to be studied. OBJECTIVES The main objective of this study was to determine the effect(s) of HAART on cognitive performances of adult Nigerians with HIV/AIDS presenting at the University of Benin Teaching Hospital, Benin City using neuropsychological test batteries. The specific aims were to compare the cognitive performances before and 12 months after institution of HAART and to determine the impact of improvement in CD4 cell count on cognitive function. DESIGN AND METHODS This is a prospective longitudinal cohort study, carried out at the University of Benin Teaching Hospital between March 2008 and August 2009. Six-nine HIV- seropositive antiretroviral naïve patients with CD4 count ≤ 350 cells/ul attending the HIV clinic of UBTH were recruited and followed up for twelve months. Their baseline cognitive performances before commencing HAART were assessed and compared with their performances after 12 months on HAART using the International HIV dementia scale (IHDS), the Community Screening Interview for Dementia (CSID) and Iron Psychology (acronym ‘Fepsy’ – a computerassisted test battery) as neuropsychological test instruments. RESULTS Sixty–nine subjects completed the study comprising of 45 (65.20%) females and 24 (34.80%) males. The mean age of the subjects was 36.2 ± 8.7 years (p>0.05). The CD4 count after 12 months on HAART was 263.43 ±148.80 cells/ µl and it was significantly higher than the mean baseline CD4 count of 136.25 ± 85.65cells /µl, t= -5.678, p=0.000 . The mean CSID score of the patients at baseline (pre-HAART) was 61.05±9.76. This was not significantly less than the control mean of 62.66 (t= -1.333, p=0.18). The mean CSID score of the patients after 12 months on HAART was 68.23± 7.85, and this was significantly better than the pre-HAART CSID score ,t= -4.410, p=0.000. It was also significantly higher than the cut-off point for the controls, t=5.66, p=0.000. The mean IHDS score before HAART (6.70 ± 2.51) was significantly less than the mean IHDS score for the control (10.5), t=15.075, p=0.000. The mean IHDS score after exposure to HAART (10.30± 2.51) was significantly higher than the pre-HAART IHDS score of the patients (6.70 ± 2.51), t= -10.58, p=0.000. It was however, not significantly different from the control mean (10.5), t= -1.309, p=0.195. The mean pre-HAART scores on Fepsy were significantly poorer than the controls at baseline p<0.05.The mean post exposure scores on Fepsy were all significantly different from the pre-HAART scores (p<0.05) except the tapping task that was not (p>0.05). The mean post-exposure to HAART scores on FePsy were also significantly better than the control means except for binary choice sensitivity and memory recognition for figures which were not significantly different p<0.05. CONCLUSION Significant cognitive impairments are associated with HIV/AIDS. Highly active antiretroviral therapy (HAART) significantly improves cognitive performances in adults with HIV/AIDS. HIV+ individuals on HAART recover from immunosuppression as demonstrated by the rise in CD4+ cell count levels. There is no correlation between the immunological recovery following HAART and the improvement in cognitive performance (β-coef of CSID2=1, β-coef of CD4ii=0.118, p= 0.38 and β-coef of IHDS2= 1, β-coef of CD4ii=0.034, p=0.80). Appropriate ARV combination therapy is recommended early in selected patients with HIV/AIDS