We have previously reported a retrospectively constructed index which can accurately predict survival at the time of diagnosis of symptomatic metastatic breast cancer. The index, derived from a Cox model, is scored: Index score = (4 x Grade)-(6 x ER) + (4 x SIMD)-(0.1 x DFI), where histological grade is scored 1-3 (good, moderate, or poor), oestrogen receptor (ER) is scored 0 (negative) or 1 (positive), site of initial metastasis (SIMD) is scored 1-4 for bone only, lung only, bone and lung, or visceral metastases, respectively, and disease-free interval (DFI) is measured in months. Patients were divided into three prognostic groups on the basis of index score. In the present study we have tested this index prospectively on a new group of 147 patients with metastatic breast cancer. The percentage of patients in each of the three groups was similar between the retrospective and prospective studies. In the prospective study the difference in survival between the 3 groups was highly significant (p less than 0.001), confirming our retrospective analysis. No single one of the four factors was as powerful in predicting survival as the index itself. We now use this index in our patient management.