Follow-up data of 320 multiple myeloma (MM) patients entering the German Myeloma Treatment Group (GMTG) trial MM01 were analysed for factors predicting overall (OAS) and tumour related survival (TRS). Response to primary induction chemotherapy was relevant for prognosis if a limit of 25% tumour cell mass (TCM) reduction was used to separate responders from non-responders. Furthermore, TCM, histological grading of myeloma cells, degree of bone marrow infiltration, haemoglobin, platelet counts, calcium, creatinine, albumin, beta 2M, and Bence Jones proteinuria correlated to both OAS and TRS. Age was relevant for OAS only. The multivariate analysis revealed histological grading, TCM and platelets as the most reliable prognostic factors. Based on these data the Durie/Salmon classification could be improved by defining poor prognosis patients (50% TRS: 16 months) characterised by pretreatment platelets of < or = 150,000 and/or poorly differentiated myeloma cell morphology. Patients lacking both risk factors displayed 50% survival times of 46 months in stage III and 88 months in stage II.