The objective of this study was to assess the efficacy and safety of a leech therapy for patients with a head and neck free tissue transfer in whom flap viability is threatened because of surgically unsalvageable venous obstruction. Of the 450 free tissue transfers to the head and neck region from January 1, 1995, to October 31, 2000, eight patients (1.8%) developed venous obstruction not considered salvageable by conventional surgical or thrombolytic therapy. All eight patients were placed on a protocol using leeches (Hirudo medicinalis), intensive care unit monitoring, antithrombotic pharmacotherapy, frequent haematological evaluation, blood transfusions as needed and antibiotic prophylaxis for Aeromonas hydrophila. All eight flaps survived with the application of this protocol. An average of 215 leeches were used per patient, and the average time needed for inosculation was 6.6 days. The average duration in the intensive care unit was 9.6 days. The morbidity was substantial, with intensive care unit psychosis, prerenal azotaemia, and large transfusion requirements being the most frequent complications. The authors concluded that aggressive application of the leech therapy presented could salvage free tissue transfers with venous obstruction that are otherwise unsalvageable.