A 30-year old male was admitted to the hospital with extremely painful blueish discoloration of his toes. After clinical and laboratory evaluation the diagnosis of a blue toe syndrome due to primary antiphospholipid syndrome (APS) was made. Complete resolution of the blue toe syndrome occurred within 72 hours following 9 mg phenprocoumon. APS consists of the association of lupus anticoagulant or antiphospholipid antibodies with arterial or venous thrombosis, thrombocytopenia, and spontaneous abortion. The exact pathways leading to thrombosis are still unknown. Our group has previously proposed that membrane-associated immune complexes contribute towards clinical symptoms in the antiphospholipid syndrome. The case presented strengthens that concept.