The purpose of this study was to assess the relationship between oral mucositis (OM) and adverse clinical and economic outcomes of autologous hematopoietic stem-cell transplantation (HSCT) following high-dose melphalan (Alkeran) conditioning in patients with multiple myeloma. A retrospective study of 115 consecutive autologous HSCT recipients with multiple myeloma who received high-dose melphalan conditioning before transplantation was undertaken at a single academic center. OM severity was assessed twice weekly using a validated scale beginning 3-4 days following conditioning and continuing until hospital discharge or day 28, whichever occurred first. OM was graded, based on presence/extent of erythema/ulceration across eight oropharyngeal sites, as follows: 0 = no erythema or ulceration; I = erythema but no ulceration; II = ulceration, 1 site; III = ulceration, 2 sites; IV = ulceration, 3 sites; and V = ulceration, > or = 4 sites. Analyses examined the relationship between worst OM grade and selected clinical and economic outcomes, including days with fever, days of total parenteral nutrition (TPN),days of parenteral narcotic therapy, incidence of significant infection, and inpatient days and charges. The mean age of study subjects was 54 years; 19 patients (17%) received total-body irradiation, and 55 patients (48%) experienced OM grade > or = II (ie, ulceration). The worst OM grade was significantly (P < 0.05) associated with numbers of days of TPN and parenteral narcotic therapy, length of hospitalization, and total inpatient charges. Worst OM grade was not associated with the number of febrile days or the risk of significant infection. OM is associated with worse clinical and economic outcomes in multiple myeloma patients undergoing autologous HSCT following high-dose melphalan conditioning.