To define outcome data and prognostic criteria for patients with metastatic renal cell carcinoma (RCC) treated with interferon-alfa as initial systemic therapy. The data can be applied to design and interpretation of clinical trials of new agents and treatment programs against this refractory malignancy. Four hundred sixty-three patients with advanced RCC administered interferon-alpha as first-line systemic therapy on six prospective clinical trials were the subjects of this retrospective analysis. Three risk categories for predicting survival were identified on the basis of five pretreatment clinical features by a stratified Cox proportional hazards model. The median overall survival time was 13 months. The median time to progression was 4.7 months. Five variables were used as risk factors for short survival: low Karnofsky performance status, high lactate dehydrogenase, low serum hemoglobin, high corrected serum calcium, and time from initial RCC diagnosis to start of interferon-alpha therapy of less than one year. Each patient was assigned to one of three risk groups: those with zero risk factors (favorable risk), those with one or two (intermediate risk), and those with three or more (poor risk). The median time to death of patients deemed favorable risk was 30 months. Median survival time in the intermediate-risk group was 14 months. In contrast, the poor-risk group had a median survival time of 5 months. Progression-free and overall survival with interferon-alpha treatment can be compared with new therapies in phase II and III clinical investigations. The prognostic model is suitable for risk stratification of phase III trials using interferon-alpha as the comparative treatment arm.