The neck dissection technique has been precisely defined. It allows resection of lymph node groups, comprising at least groups IIA, IIB, III and IV according to Robbins’ classification for head and neck cancer. Neck dissection is classically performed in an upwards and forwards direction, but the technique can vary according to the site of lymph nodes. The authors describe the central role of dissection of the triangle between the spinal accessory nerve and the internal jugular vein at the beginning of neck dissection in order to facilitate group IIB dissection while avoiding traction on the spinal accessory nerve and to ensure early control of the internal jugular vein superiorly; release of the vein also facilitates subsequent dissection of the thyrolinguofacial trunk and identification of the hypoglossal nerve. This specific dissection and its role has not been previously described in the literature. This triangle constitutes the posterior part of group IIA, but is intimately related anatomically to group IIB dissection.