Possible pathogenetic processes in sickle cell disease include antioxidants, endothelial and platelet changes, and hypercoagulability. Hypothesizing relationships between these processes, we recruited 47 young adult patients (mean age 19 years) with homozygous sickle cell disease and 40 age-, race- and sex-matched healthy controls and measured plasma markers representative of these processes. We found raised plasma von Willebrand factor (P = 0.001) and intercellular adhesion molecule (P = 0.016, both marking endothelial perturbation, but the latter also marking inflammation), raised soluble P selectin (P = 0.002) (marking platelet activation) and inflammation marker C reactive protein (P = 0.021), but reduced antioxidant capacity (P = 0.002) in patients compared with controls. There was no difference in fibrinogen and there was no significant correlation between any of the indices. Our data suggest that changes in endothelial and platelet function in sickle cell disease are unrelated to reduced antioxidant capacity.