Skin ulceration is a well-characterized thrombotic complication of the heparin-induced thrombocytopenia (HIT) syndrome. We present the case of a 73-year-old diabetic woman nearing end-stage renal failure who developed extensive upper thigh, abdominal and buttock ulceration following initiation of subcutaneous heparin for prophylaxis against deep vein thrombosis. A preliminary diagnosis of calciphylaxis was made based on the classical distribution and macroscopic appearance of the ulceration in a patient with end-stage renal failure and secondary hyperparathyroidism. However skin biopsy showed complete absence of calcium deposits in the dermal microvasculature. The presence of extensive microthrombi within dermal vessels prompted serologic testing to detect a prothrombotic state. We identified the combined presence of heparin-dependent platelet activating (HIT) antibodies and functional protein S deficiency. To our knowledge this is the first reported case of a dialysis patient presenting with skin ulceration induced by heparin and protein S deficiency. This case highlights the importance of a skin biopsy and testing for a hypercoaguable state in patients with end-stage renal disease and skin ulceration. We suggest that HIT antibodies should be requested in all dialysis patients presenting with skin ulceration.