Koo et al1 reported an interesting study confirming that major bleeding associated with excessive anticoagulation with warfarin is also associated with an increase in mortality compared with nonexcessive anticoagulation. They state that their study findings confirm that errors in drug monitoring are the main cause of excessive anticoagulation. Although this is a logical conclusion to reach, it is not supported by the published results. I would be interested to see if they had collected data on international normalized ratio (INR) monitoring prior to the major bleeding event to ensure that adequate monitoring had been performed.