Patients with lupus nephritis frequently exhibit increasing proteinuria, hypertension and deterioration of renal function due to either active lupus nephritis, chronic lupus nephritis and/or superimposed preeclampsia during pregnancy. Percutaneous renal biopsies were therefore performed in 3 women with systemic lupus erythematosus during pregnancy and immediately postpartum in a fourth woman to evaluate their renal disease during pregnancy. Mean serum creatinine at renal biopsy was 2.9 mg/dl, with a mean creatinine clearance of 66 ml/min and protein excretion of 5.3 g/day. All patients had grade IV lupus nephritis and received pulse methylprednisolone immediately; 3 received cyclophosphamide. All 3 patients with crescent formation developed end-stage renal disease within 3 years. The fourth patient has normal renal function 3 years after biopsy. Percutaneous renal biopsies during pregnancy in women with lupus nephritis provide an accurate histopathologic diagnosis and are important in providing appropriate therapy, counseling and prognosis.