OBJECTIVE To report three cases of a suspected interaction between warfarin and fluvastatin. METHODS Three patients receiving stable warfarin dosages with therapeutic international normalized ratios (INRs) exhibited increased INRs when fluvastatin was added to their maintenance regimens. While none of the patients experienced a bleeding episode, they did require a reduction in their weekly warfarin dosage to achieve an appropriate level of anticoagulation. CONCLUSIONS Reports of an interaction between warfarin and lovastatin have been described previously; however, to our knowledge, this is the first published report of a possible interaction between warfarin and fluvastatin. These cases were chosen because other factors that could potentially increase the INR were ruled out as significant contributors. CONCLUSIONS The exact mechanism for the potential interaction between warfarin and fluvastatin is unknown. Until more is known, it is advisable to monitor patients more frequently when fluvastatin is initiated, discontinued, or adjusted in patients taking warfarin.