This paper reports the case of an adult patient with severe protein C(PC) deficiency. She had the first deep vein thrombosis when she was 14 years old and developed skin necrosis when oral anticoagulant treatment was started. The same sequence of thrombotic complications recurred several times. Analysis of the PC gene coding sequences allowed two mutations (Arg-1 to His and Arg 178 to Gln) to be identified in this compound heterozygote. Oral anticoagulant treatment during PC concentrate infusion and low-molecular-weight heparin administration was successful and uncomplicated.