The course of pregnancy in patients with systemic lupus erythematosus is not known. The Hopkins Lupus Pregnancy Center has followed 64 patients (74 pregnancies) prospectively since 1987. Patients are seen monthly and clinical and pregnancy-related data collected, with particular emphasis on the occurrence of lupus flare. Flare rate during pregnancy was 1.63 per person-year, compared to 0.64-0.65 after delivery or in non-pregnant patients. Flare did not influence pregnancy outcome. Low serum C3 or C4 and high anticardiolipin antibody predicted pregnancy loss, and prednisone dose, aspirin use, diastolic second trimester blood pressure, C3 at first visit, and race predicted preterm birth. Maternal flare and preterm birth are important risks in lupus pregnancy. The latter can be predicted from maternal pregnancy data.