Thrombosis due to heparin-induced thrombocytopenia (HIT) is rare but has a severe prognosis. Its management is not always easy, particularly in old patients with renal insufficiency. A 95-year-old woman was hospitalized for dyspnea. Curative treatment with unfractionated heparin was started because pulmonary embolism was suspected. Disseminated intravascular coagulation was then suspected because of thrombocytopenia, hypoprothrombinemia, hypofibrinogenemia, and a positive ethanol gelation test. The first immunoassay for HIT was negative. On the 12th day of hospitalization, bilateral cyanosis of the toes occurred associated with recent deep bilateral venous and arterial thrombosis at duplex ultrasound. New biological tests confirmed HIT and led us to stop heparin and to start argatroban with a positive clinical and biological evolution. Venous and arterial thrombosis associated with thrombocytopenia during heparin treatment must be considered HIT whatever the biological test results are. Argatroban is a good alternative treatment in the elderly.