In August 1994, a 19-year-old woman presented to her dermatologist with a slight fever, arthralgia, and a butterfly rash. Discoid lupus erythematosus was suspected, and serological testing yielded positive results for antinuclear antibody. She was diagnosed with systemic lupus erythematosus without organ failure and was treated with only nonsteroidal antiinflammatory drugs. She became pregnant in June 2001, at age 26. In November her obstetrician noted that she had severe hypertension, edema of the low limbs, and proteinuria. On admission, she was diagnosed with severe preeclampsia, and cesarean section was performed. On hospital day 3 the patient developed sudden epigastric pain and vomiting. Laboratory tests revealed thrombocytopenia, liver dysfunction, and microangiopathic hemolytic anemia, leading to a diagnosis of HELLP (hemolysis, elevated liver enzymes, and low platelet count) syndrome. Plasma exchange was performed for 5 days. The thrombocytopenia, liver dysfunction, and proteinuria diminished quickly. Later testing revealed a high titer of plasma phosphatidylserine-dependent anti-prothrombin antibody. This case is useful for exploring the relations between SLE, HELLP syndrome, and anti-prothrombin antibody.