Clinical and serological records of 865 patients with confirmed autoimmune haemolysis (AIH)--a much larger series than any previously reported--were critically reviewed nd analysed. A proposed new classification for AIH based on serological findings differs from traditional classifications in that a new category of "mixed" AIH has been defined in which both "warm" and "cold" autoantibodies are present, and both are capable of causing haemolysis. Patients in this mixed group tend to have severe disease that may run a chronic intermittent course. The presentation of cold agglutinin disease is much more variable than has been seen in previous studies, haemolysis due to low titre autoantibodies being common. The AIH associated with pregnancy, usually considered as being of bad prognosis, is often mild and self limiting in the absence of other associated disorders.