A 20 year old female patient with anti-phospholipid antibody syndrome who presented chorea as an initial symptom is described. At the age of 14, she noticed involuntary movements of upper and lower extremities bilaterally. The CT scan revealed the presence of low density areas in the right caudate nucleus and left putamen. The result of the laboratory tests included antibodies to nuclear antigens (positive FANA and anti-DNA), prolonged PT and APTT, biological false positive for syphilis. Her serum contained antibodies to cardiolipin and phosphatidylserine as demonstrated by specific ELISA assay method. The clinical diagnosis of chorea was made and haloperidol was administered with partial symptomatic improvements. The patient reported here is the first well documented case of anti-phospholipid antibody syndrome presenting chorea as an initial manifestation in the Japanese literature.