High-dose therapy has become a common treatment for myeloma. The objectives of this study were to estimate in a prospective, population-based setting the impact on survival of high-dose therapy in newly diagnosed, symptomatic patients less than 60 years old and to compare the results with those of conventionally treated historic controls. The prospective population comprised 348 patients. Of these, 274 were treated according to a specified intensive-therapy protocol (Nordic Myeloma Study Group [NMSG] #5/94) and constituted the intensive-therapy group. The historic population consisted of 313 patients identified from 5 previous population-based Nordic studies. Of these, 274 fulfilled the eligibility criteria for high-dose therapy stated in NMSG #5/94 and constituted the control group. The expected numbers of patients in the prospective population and the historic population were 450 and 410, respectively, estimated from previously established data on the incidence in this population and the population base for each study. Survival was prolonged in the intensive-therapy group compared with the control group (risk ratio for the control group 1.62; 95% confidence interval 1.22-2.15; P =.001). These groups represented more than 60% of the expected number of patients. When survival for all the registered patients in the 2 populations was compared, representing more than 75% of the expected number of patients, the advantage for the prospective population persisted (risk ratio for the historic population 1.46; 95% confidence interval 1.14-1.86; P =. 002). These results indicate that the introduction of high-dose therapy for newly diagnosed myeloma has resulted in prolonged survival for the total patient population aged less than 60 years. (Blood. 2000; 95:7-11)