Abstract AIM: To describe the computed tomography (CT) findings associated with active bleeding from the internal mammary artery (IMA) in blunt trauma victims and to assess complications related to IMA haemorrhage. MATERIAL AND METHODS: All cases of active IMA haemorrhage identified in blunt trauma patients on admission CT were identified from a trauma radiology data base covering 1990–1999. Computed tomography examinations, operative and medical records were reviewed to ascertain CT findings, complications, and patient outcome. The determination of active bleeding required CT evidence of a central contrast blush of CT density within 10 HU of an adjacent artery surrounded by haematoma. RESULTS: Four patients with CT evidence of active IMA haemorrhage were identified. All cases had surgical confirmation of an IMA source of haemorrhage. There were three patients with unilateral and one patient with bilateral IMA disruption. Three patients exhibited clinical signs of cardiac tamponade related to compression of one or more cardiac chambers by the anterior mediastinal haematoma. Sudden clinical deterioration compatible with tamponade developed in all three patients. CONCLUSION: Early CT recognition of active bleeding within the chest can direct rapid surgical or angiographic intervention. On-going blood loss and, in particular, the threat of cardiac tamponade must be considered with IMA injury.Braatz, T. (2001). Clinical Radiology 56, 120–123.