A group of 73 patients with advanced renal cell carcinoma, treated in different phase II trials with interferon alpha and/or interleukin-2, have been evaluated to identify potential baseline prognostic factors predicting their survival. The eligibility criteria were very similar across studies and included ECOG performance status < or = 2, measurable or evaluable disease and no CNS metastases. The overall response rate was 8%. The overall survival was 33% at 2 years and 18% at 1 year. In the univariate analysis three prognostic factors were correlated with disease outcome: ECOG performance status (0 versus > or = 1), time from diagnosis to treatment (< or = 12 months versus > 12 months) and number of metastatic sites (1 versus > or = 2). Multivariate analysis identified ECOG performance status and number of metastatic sites as important prognostic factors for survival. The true impact on patient survival of the selection of patients rather than the treatment itself should be evaluated in controlled trials.