In a retrospective study we have sought to determine whether the administration of angiotensin-I-converting enzyme inhibitors (ACEI) influences the outcome of patients with multiple myeloma (MM). Patients with MM who underwent autologous peripheral blood stem cell transplantation (PBSCT) (n=168) were studied. Patients taking ACEI alone or in combination with other antihypertensive agents during the hospital admission for PBSCT were allocated to the ACEI group (n=25; 15%). Patients from the non-ACEI group (n=143; 85%) were taking other or no antihypertensive medication. Patients taking ACEI had worse overall survival (OS) compared to patients not taking ACEI (38.7 versus 73.3 months after diagnosis; P=0.025). Among patients with hypertension, both OS and progression-free survival were significantly shorter in patients taking ACEI. There were no significant differences between the studied groups in standard prognostic parameters for MM (age, albumin, beta 2-microglobulin, IPI and Durie-Salmon stage, LDH, CRP, performance status) or in engraftment. The mortality in our study has been mostly myeloma related. In conclusion, according to our findings, ACEI administered during PBSCT have adverse effect on survival of patients with MM.