Improvement in the reliability of the lower transverse rectus abdominis musculocutaneous flap for breast reconstruction using autogenous tissues has been predicated on a thorough analysis of the vascularization of this flap and methods for its preservation. The arbitrary division of the skin paddle into zones based on relative perfusion has simplified an appreciation of the underlying vascular anatomy. Laser Doppler flowmetry has been used to confirm these anatomical findings and establish a single system based on descending values of observed blood flow. Zone I has been assigned to that region overlying the ipsilateral and zone III the contralateral rectus sheath, whereas zone II corresponds to the ipsilateral and zone IV the contralateral superficial inferior epigastric territory.