Introduction: The internal mammary and thoracodorsal vessels are the standard recipient vessels for free flap breast reconstruction. Recently, several groups have reported use of the internal mammary perforators as alternate recipient vessels for free flap breast reconstruction. Palmer and Taylor mapped the vascular territories of the anterior chest wall, but did not report the diameter of the perforator vessels. The purpose of this study is to analyze the diameters of the internal mammary perforating vessels. Methods: Ten fresh cadavers were dissected through an anterior midline presternal incision. Using a micrometer under loupe magnification, bilateral measurements were taken of the first five internal mammary perforators and the internal mammary vessels between the second and third ribs. Results: The ten dissected cadavers (8 female, 2 males) had an average age of 80.6 years. The external diameter of the arterial perforators averaged 1.14mm (SD=0.50, range 0.3-2.7). The venous perforators also had an average external diameter of 1.14mm (SD=0.62, range 0.25-3.5). When only the largest perforators from each side were evaluated, the artery averaged 1.74mm (SD=0.45, range 1.1 to 2.7mm). The veins of the largest perforators averaged 1.78mm (SD=0.78, range 0.75 to 3.5mm). The largest perforators were most frequently found in the second and third rib spaces. Conclusion: Every cadaver had perforators which measured at least 1mm in diameter. The largest perforators appeared adequate for microsurgical anastomosis and were most frequently found in the second or third rib space. Advantages to the use of the internal mammary perforators include; decreased time to expose recipient vessels, no rib resection (thus no potential pneumothorax and/or contour deformity), preservation of the internal mammary artery for use in coronary revascularization and no need to perform microsurgery in a hole between ribs. Certainly, the reconstructive breast surgeon will need excellent cooperation from the oncologic surgeon to preserve these perforators during mastectomy. This study has elucidated a protocol which we recommend for recipient vessel dissection: map the perforators with doppler, search for an adequate perforator in second and third rib space, and be prepared for partial rib resection to expose the internal mammary vessels if needed.