We investigated in a retrospective multicenter study the impact of chromosome arm 13q deletion (13q-) as detected by fluorescence in situ hybridization (FISH) on outcome after dose-reduced allografting in patients with multiple myeloma. In 68 of 140 patients, data on chromosome 13q status were available. Most patients included had advanced myeloma. At 2 years, patients with 13q deletion (n = 31) had a shorter event-free (18% vs 42%; P =.05) and overall survival (18% vs 67%; P =.03) than patients without 13q- (n = 37). Patients with 13q- experienced a higher relapse rate (77% vs 44%; P <.001) but a similar incidence of transplantation-related mortality at one year (24% vs 18%). In a multivariate analysis, 13q- remained a significant risk factor for a higher relapse rate (hazard ratio [HR], 3.28; 95% confidence interval [CI], 1.31-8.24; P =.01) and a shorter event-free survival (HR, 1.94; 95% CI, 1.03-3.67; P =.04). Concerning overall survival, 2 or more cycles of prior high-dose chemotherapy were associated with a significantly higher probability of death (HR, 2.48; 95% CI, 1.19-5.17; P =.02), while patients with deletion 13q had a nearly 2 times higher risk of death (HR, 1.94; 95% CI, 0.95-3.98; P =.07) after dose-reduced allogeneic stem cell transplantation.