Warfarin, a commonly prescribed anticoagulant, has a narrow therapeutic index; and is metabolised by a number of cytochrome P-450 isoenzymes. Fluvoxamine is an effective antidepressant. It is a potent SSRI, with proven efficacy on obsessive-compulsive symptoms, anxiety, and psychotic depression. It is also a potent inhibitor of a number of cytochrome P-450 isoenzymes and has the potential to cause pharmacokinetic interactions with warfarin, resulting in elevated International Normalised Ratio (INR). We report a case of an elderly man, who was on warfarin for atrial fibrillation. He also suffered from severe and complex depressive episodes, with marked anxiety, and obsessive-compulsive symptoms which at times were impervious to reassurance and rational explanations. The depression responded inadequately to a number of trial of antidepressants, including a combination of antidepressants. Hence a decision was taken to commence Fluvoxamine. Co-administration resulted in the marked and rapid elevation of INR, necessitating adjustment in the dose of Warfarin. Although Fluvoxamine, by dint of its pharmacokinetic profile as a Selective Serotonin Reuptake Inhibitor (SSRI) has a high likelihood of interaction with Warfarin, there are very clinical few case-reports of such an interaction. Over the years, the use of Fluvoxamine in clinical practice has declined following the availability of other SSRIs that have less effect on the cytochrome enzyme system. However, in certain clinical situations where the use of Fluvoxamine is warranted, careful consideration of the drug interactions is highly recommended The case demonstrates the necessity of close monitoring when Fluvoxamine is co-administered with Warfarin, as the INR is elevated and the risk of haemorrhage increases even at small doses of Fluvoxamine. This close monitoring becomes even more relevant in the elderly because of prolonged half-life of Fluvoxamine in this population.