Objective: This work was designed to study the impact of HIV and anti-retroviral therapy on some haematological and haemorheological parameters. Method: Two hundred and fifty three subjects aged 18 __ampersandsignndash; 60 years; comprising; 85 HIV patients on ART, 90 not on ART and 78 age-matched apparently healthy HIV negative controls were recruited. CD4+ count, Haematocrit, Mean corpuscular volume (MCV), Mean corpuscular haemoglobin (MCH), Mean corpuscular haemoglobin concentration (MCHC), red cell distribution width (RDW), Whole blood viscosity (WBV), plasma viscosity (PV) and plasma fibrinogen were assayed. Result: WBV, PV, plasma fibrinogen, RDW and MCV were significantly higher in HIV-positive subjects on ART and those not on ART compared to the controls (p__ampersandsignlt;0.05). While HCT and CD4+ count, were significantly lower in HIV-positive subjects on ART and those not on ART compared to the controls (p__ampersandsignlt;0.05). MCH and CD4 count were significantly higher in HIV subjects on ART than non-ART subjects (P__ampersandsignlt;0.05). MCV was significantly higher in female than males on ART and non-ART (P__ampersandsignlt;0.05). HCT was significantly higher in males than females in subjects not on ART and the control subjects (P__ampersandsignlt;0.05). Plasma fibrinogen was significantly higher in females than males on ART and control subjects while MCH and CD4 count were higher in male than female control subjects (P__ampersandsignlt;0.05 respectively). Conclusion: The increase in WBV, PV and Plasma fibrinogen indicates an altered haemorheology while the decrease in HCT, MCH and MCHC is a pointer to anaemia known to be prevalent in HIV patients. The reduction in CD4 indicates the immunosuppressed state of the patients.