Adverse prognostic factors in multiple myeloma include advanced age, number of prior therapies, and higher International Staging System (ISS) disease stage. In the international, randomised, phase-3 Assessment of Proteasome Inhibition for Extending Remissions (APEX) study, bortezomib demonstrated significantly longer time to progression (TTP), higher response rates and improved survival compared with high-dose dexamethasone in patients with relapsed multiple myeloma following one to three prior therapies. In this APEX subgroup analysis, efficacy of bortezomib and dexamethasone was compared in elderly (age > or =65 years) and high-risk (>1 prior line of therapy; ISS stage II/III; refractory to prior therapy) patients. Bortezomib demonstrated substantial clinical activity in these patients. Response rate (34-40% vs. 13-19%), including complete response rate (5-8% vs. 0-1%), was significantly higher with bortezomib versus dexamethasone in all four subgroups. Similarly, median TTP was significantly longer with bortezomib versus dexamethasone, and 1-year survival probability was significantly higher in all subgroups. As in the total APEX population, rates of grade 3/4 adverse events were higher in bortezomib- versus dexamethasone-treated patients aged > or =65 years and with >1 prior line, while rates of serious adverse events were similar; toxicities generally proved manageable. Bortezomib should be considered an appropriate treatment for elderly and high-risk patients with relapsed multiple myeloma.