The clinical and serological records of 20 pregnant patients with erythrocyte autoantibodies were critically reviewed and analysed. This series, the largest reported, confirmed an association between erythrocyte autosensitization and pregnancy, and suggested that this occurred on an average of 1 in 50,000 pregnancies. The clinical presentation varied from severe haemolytic anaemia to serological abnormalities discovered during the routine testing of well patients; overt haemolysis was present in 7 cases. Treatment was only necessary in 3 patients where the haemolysis was severe. 3 infants were mildly affected with haemolytic disease due to the maternal autoantibodies crossing the placenta but no treatment was needed. The risks to the infant were increased when other active autoimmune conditions (e.g., systemic lupus erythematosus) were present. With early diagnosis and appropriate treatment, the outlook for mother and child is good.