We analyzed the incidence, etiology, risk factors and outcomes of 49 episodes of pneumonia that developed in 326 adult patients undergoing autologous stem-cell transplantation (ASCT) from January 1990 to December 2005. The median time for the onset of pneumonia after transplantation was 11 days (range 0 - 148). Empirical antibiotic therapy in patients with pneumonia consisted of piperacillin - tazobactam (20 cases, 49%), third-generation cephalosporin (11 cases, 27%) and carbapenem (8 cases, 19%). Multivariate analysis showed that a higher risk of pneumonia could be predicted for patients with myeloma (P = 0.006) and for patients with an absolute neutrophil count <0.5 × 109 L >7 days (P = 0.008). Cumulative incidence of transplant-related mortality at 6 months was 51% versus 8% for patients with or without pneumonia, respectively (P = 0.001). Pneumonia after ASCT is a severe complication more commonly observed in patients with myeloma and with prolonged duration of neutropenia.