High-dose melphalan at 200 mg/m2 can be administered in 1 day or over 2 consecutive days before autologous hematopoietic cell transplantation (HCT) for multiple myeloma (MM). Limited data exist on the comparison of the two dosing schedules. A retrospective study of 278 consecutive MM patients receiving high-dose melphalan from January 2010 to December 2012 was conducted. Objectives were to compare the length of hospitalization, toxicity profile, response rates, PFS and OS. One hundred and eighty five patients received 2-day dosing and 93 received 1-day dosing. The two end points of the 95% confidence interval (CI) for the difference did not exceed the preselected margin, therefore the length of hospitalization was considered equivalent. No significant differences were found for response rates, PFS and OS. The toxicity profile was similar with the exception of more frequent ≥ grade 3 oral mucositis in the 2-day group (13.5% vs 5.4%; odds ratio 3.07 (95% CI:1.11-8.48); P = 0.03). High-dose melphalan, given either in 1 day or over 2 days, produced comparable treatment outcomes except for increased grade 3/4 mucositis in the 2-day regimen. One-day dosing could shorten the hospital stay by 1 day and may allow better resource utilization.