3D image technology provides a very effective tool for evaluating, characterising, and drawing up the surgical treatment plan for potential orthognathic surgery patients. Patients with dysmorphic syndromes or incorrect jaw positions frequently show facial asymmetry. The objective of this cross-sectional survey is to evaluate facial asymmetry by means of three-dimensional computed tomography (CT) reconstructions. Twenty one consecutive patients were diagnosed using a CT scan. 3D reconstructions of the patients' skulls were made and then measurements taken of different craniometric landmarks and of the various structures presenting asymmetry. The gonion emerged as the most asymmetrical point in all subjects, and the anterior nasal spine showed least deviation. The t test produced statistically significant differences (p < 0.05) between symmetric and asymmetric patients at all landmarks. The lateral inclination of the mandibular ramus was shown to present the greatest asymmetrical deviation, followed by the frontal inclination of the mandibular ramus. The angulation of the mandibular ramus, on both frontal and lateral planes, determines apparent facial asymmetry, as well as conditioning the surgical treatment plan for patients with craniofacial asymmetry.