One of the common complications of sickle cell disease is the vaso-occlusive crisis or sickle cell crisis which could result in impaired oxygen delivery to the tissues. This study investigates the oxygen delivery index (ODI) in 38 patients with homozygous sickle cell anaemia. Thirty-three patients were in the steady state and five were experiencing crisis at the time of recruitment. Whole blood viscosity was measured with a Wells Brookfield viscometer at a shear rate of 230 sec(-1) and haematocrit was measured with an AC Tron Coulter Counter. The ODI, which is an indirect measure of the capacity of blood to deliver oxygen to tissues, was calculated as the ratio of haematocrit to whole blood viscosity values. There was no statistically significant difference in the ODI between the steady and crisis states, suggesting that tissue oxygenation is not the only factor involved in the sickle cell crisis.