Haemolytic uraemic syndrome thrombocytopenic thrombotic purpura (HUS/TTP) remains an incompletely understood complex disease process that involves many organs. It was first described, as thrombocytopenic purpura, by Moschcowitz in 1924 (1). Since that time the prognosis of this disease has improved considerably, the short term mortality declining from 90% to 10%. Challenging questions remain, however, about clinical classification, pathophysiology, and therapy of the initial episode and later relapse. The present art and science of classification, pathophysiology and therapy, plus recommendations for future approaches are presented in this paper.