Few studies have evaluated prognostic factors among patients with multiple myeloma (MM) since new therapies have become available. Monthly zoledronic acid (ZOL) has been incorporated into many treatment regimens to reduce skeletal-related events (SREs), but outcomes among patients receiving this bisphosphonate have not been well-defined. The aim of this retrospective study was to determine baseline and on-treatment prognostic factors in these patients. Data were collected from the date of diagnosis on 300 consecutive MM patients treated with ZOL. Median duration of ZOL was 18 months (range 1–121 months). The skeletal morbidity rate was 0.116 events per patient year. Five-year overall survival (OS) was 69%. Risk factors for shortened OS included SREs, increased serum creatinine, and International Staging System (ISS) Stage II or III. Thirty-four (11%) patients showed worsening renal function. In 28 of these patients, ZOL was discontinued and restarted in half of these patients following a brief delay. Only 5 of the 34 patients showed worsening of their renal function. Fourteen patients (4.7%) developed osteonecrosis of the jaw (ONJ). All patients with ONJ are in remission or with stable disease except one patient who died of a myocardial infarction while in remission. Only two patients showed some worsening of ONJ despite of ongoing monthly ZOL. Overall, these results suggest that skeletal complications are an important prognostic factor for MM. Although ONJ and renal deterioration may infrequently occur with ZOL, most patients do not experience worsening of these conditions with ongoing treatment with this bisphosphonate. Am. J. Hematol., 2011. © 2010 Wiley-Liss, Inc.