A retrospective analysis was made of 14 consecutive adults with hemolytic uremic syndrome/thrombotic thrombocytopenic purpura (HUS/TTP) who were treated with plasma exchange (PE). In six patients the disease was primary, whilst in eight HUS/TTP was considered secondary to an associated condition. Thirteen patients had renal involvement, six had central nervous system symptoms or signs, three had fever, and one had myocardial damage. Twelve patients (86%) recovered. Four of these relapsed, but responded to further treatment. Two patients failed to respond and died. Hematological response occurred rapidly in survivors: thrombocytopenia resolved after a median of four exchanges, and hemolysis after a median of six. Four patients had a complete recovery, seven had residual mild end organ damage, and one had severe renal impairment. PE was an effective treatment for both primary and secondary HUS/TTP. The platelet count proved to be the earliest indicator of clinical outcome. Continuing follow-up of survivors is required because of the risk of relapse and the high incidence of end organ damage.