Our prior research conducted under the auspices of an AHRQ-funded Center of Excellence for Patient Safety Research and Practice (PO1HS11534) demonstrated overwhelming evidence of safety problems with warfarin therapy in the nursing home setting. Based on that work, we conservatively estimate that there may be as many as 34,000 fatal, life-threatening, or serious adverse warfarin-related events per year in the nursing home setting, the majority of which may be preventable. These include both bleeds and thromboembolic events. Errors in warfarin prescribing and monitoring are responsible for nearly all of the preventable events; inadequate communication of information regarding prior international normalized ratio (INR) values and interacting medications played an important role in many of these events.