: Heparin-induced thrombocytopenia (HIT) is known for its strong association with thrombosis and distinct pathogenesis involving anti-PF4/polyanion antibodies that activate platelets strongly through clustering of platelet FcγIIa receptors. Autoimmune HIT (aHIT) refers to a subgroup of patients whose HIT antibodies have both heparin-dependent and heparin-independent platelet-activating properties. aHIT patients have atypical clinical presentations including delayed-onset HIT, persisting (refractory) HIT, heparin 'flush' HIT, fondaparinux-associated HIT, severe thrombocytopenia (platelet count <20 × 10/L) with overt disseminated intravascular coagulation, and spontaneous HIT syndrome. : This article reviews all available literature describing the use of high-dose intravenous immunoglobulin (IVIG) as an adjunct treatment to anticoagulation in HIT patients. IVIG is usually effective in interrupting platelet activation by aHIT antibodies, manifesting as a rapid platelet count increase after starting IVIG (usual dose, 1g/kg × 2 days). Experience to date suggests IVIG de-escalates HIT and likely reduces thrombotic risk. A new case of aHIT successfully treated with IVIG is presented. Use of IVIG to prevent acute HIT with planned heparin reexposure in antibody-positive patients is also discussed. : High-dose IVIG appears to rapidly inhibit HIT antibody-induced platelet activation and has the potential to become an important treatment adjunct for HIT, particularly in patients with aHIT.