The prognosis of systemic lupus erythematosus (SLE) is considerably worse when accompanied by renal involvement. In order to study the outcome within a year of histologic diagnosis of severe lupus nephritis, we obtained data on 25 patients from nine participating centers. All these patients fulfilled clearly defined histologic criteria of severe lupus nephritis, thus enabling us to evaluate a homogeneous group of patients. During a mean follow-up period of 9.4 months, there appeared to be an equal probability that the renal function would improve, remain stable, or worsen as assessed by changes in serum creatinine concentration. One patient died and another patient reached end-stage renal disease (ESRD), a combined crude mortality plus ESRD rate of 8% for 9.4 months. As both these patients had serum creatinine values of less than 2 mg/dL at the time of diagnosis of severe lupus nephritis, it appears that normal or mildly impaired renal function at the time of diagnosis does not ensure benign outcome. These features should be considered when new studies on SLE nephritis are planned or any new therapeutic modality is evaluated.