A prospective study of 110 patients with systemic lupus erythematosus (SLE) was undertaken to evaluate the reliability of clinical signs of lupus nephritis, which developed in 39 (35%) patients. Those patients with SLE who showed no clinical signs of lupus nephritis had an excellent survival rate (10 year survival 93%) and retained normal renal function (serum creatinine less than 130 mumols/l); clinical lupus nephritis developed mainly in the first three years after diagnosis of SLE and was associated with a decreased survival rate (10 year survival 62%). Increased mortality was found in male patients with lupus nephritis over 25 years of age and in female patients with lupus nephritis under 25 years of age, while renal failure rates did not differ between these groups. Treatment of lupus nephritis with high dose prednisone alone or in combination with immunosuppressants did not result in differences in patient survival or renal function preservation. It was concluded that clinical variables are a reliable guide in the management of patients with SLE, and routine use of renal biopsy in these patients is rejected.