Autologous peripheral blood stem cell transplantation (auto-PBSCT) has facilitated high-dose chemotherapy for the treatment of various types of malignancy, but the factors affecting the treatment outcome have not been well defined. We evaluated patients who underwent auto-PBSCT (46 patients with hematological malignancies and 39 with solid tumors) to elucidate the risks of background factors, including age, in association with infectious complications. In contrast to former reports, faster engraftment did not influence the incidence of documented infection or neutropenic fever, whereas high age (age > or = 50 years old) and delayed platelet recovery (> or = 18 days) were demonstrated to be positively involved. The odds ratio (OR) for documented infection in elderly patients was 4.94 (95% confidence interval, 1.22-15.8). Another risk factor of infection was the HD-ICE regimen (ifosfamide, carboplatin, etoposide) given to patients with solid tumors (OR, 8.00; 95% confidence interval, 1.61-39.7). In conclusion, we found that elderly patients and patients on the HD-ICE regimen have a higher risk of infectious complications even after auto-PBSCT. Although the clinical indications for auto-PBSCT can be extended to elderly patients, thorough precautions should be taken against infectious complications during the pre-engraftment phase.