Heparin-induced thrombocytopenia (HIT) is a not-uncommon adverse effect of heparin exposure, with potentially serious and/or fatal thrombotic consequences. Recent studies looking at the off-label use of fondaparinux for HIT show similar efficacy and adverse-effect profiles, as well as improved costs, compared with some commonly used direct thrombin inhibitors. Although routine laboratory monitoring of fondaparinux-specific anti-Xa levels typically is not recommended, we present a case report that suggests fondaparinux monitoring may be needed in patients with hepatic impairment causing acquired antithrombin deficiency. We performed daily assessment of antithrombin- and fondaparinux-specific anti-Xa levels in a 50-year-old female of unknown ethnicity to ensure that fondaparinux dosing was maintained within an acceptable range. With this management strategy, the patient experienced no thrombotic or hemorrhagic complications during the hospital admission or the following 2 months in outpatient treatment.